ZTL Center Controller reported traffic flow management issues during weather conditions.

Narrative

[It] was a bad day for air traffic controllers; pilots and passengers. Complications due to weather and inadequate staffing put a huge strain on the NAS. It created unsafe situations and pushed air traffic controllers to edge of their breaking point. The volume and complexity of the situation caused controllers to stop accepting hand offs because they could not safely take any more aircraft.Rerouting aircraft off of the east coast out of ZJX and back into ZTL created a bottleneck in the traffic flow. The receiving ZJX controller was quickly overloaded with aircraft and they shut off the ultra high sector and requested some of my aircraft to be vectored away from their airspace. This created a ripple effect. Adjacent sectors and facilities would soon be holding flights that were heading towards ZJX. This caused a major disruption in airline schedules causing canceled and delayed flights. As a result many passengers lives were interrupted. They missed vacations; weddings; funerals and business meetings. The true impact of this event is un-measurable. Not to mention the financial expense this had on the airlines. There was lost revenue and extra fuel cost associated with the longer routes and holding.I believe my experience is one shared by many controllers on this day. However; I don't think you will be hearing about the majority of them since there is a reluctance for air traffic controllers to fill out reports. You will hear from my perspective how one sectors airspace was over loaded and overwhelmed. Please keep in mind that this was also occurring in the sector above me and was a trend that continued throughout the day.Here is how things quickly went from under control to completely overwhelming in my sector. In the southeast portion of my sector there was moderate to extreme precipitation. I don't recall any pilots wanting to fly anywhere near it. We have a steady stream of aircraft flying through my airspace on normal routes to Florida and beyond to places like Mexico and the Caribbean.Without notice I start receiving numerous aircraft from the east also trying to get to Florida and the Caribbean. This was not their normal route. These flights were originally routed through Jacksonville Center sectors (J65 and J66). Now I have a steady stream from the north and a steady stream from the east trying to funnel into Jacksonville sectors (J33 and J34).Jacksonville sector (J33 and J34) was quickly over loaded. We were calling on what felt like every hand off because they were not being taken in a timely fashion. This caused a lot of our attention to be focused on that southern boundary while we tried to blend the two streams of traffic.At some point I was told that Florida was closed and ZJX was not taking anymore. This was extremely confusing because I have never heard of a state closing. What were they talking about? Florida is closed!!! Does that mean over flights or flights landing in Florida. What also added to the confusion is that ZJX was still taking some of my flights while others I was forced vectored out of my airspace into an adjacent ZTL sector. I do not know what happened to those flights.At one point I called ZJX asking them to tell me what they needed. The stress of not knowing what aircraft they would take and what aircraft needed to be vectored out took its toll on me.At some point during all this confusion I see Aircraft X northbound in conflict with Aircraft Y southwest bound. They were both at FL340.Aircraft Y was an offload and not on a normal route. As soon as I see the conflict I descended Aircraft X to FL320. No answer!!! I try again and once again no answer!!! At this point they are flashing. I don't have many options with the Aircraft Y; I can't turn him left due to the bad weather just south of him. I can't climb him because the sector above is also saturated with off loads; volume and complexity.I decided to descend the Aircraft Y since I do nonot have communications with the Aircraft X. I tell the Aircraft Y; to descend and be level in a minute or less. While I am doing this ZJX calls. I assume they see the flashing and still have radio communications with the Aircraft X. My D side then coordinates the Aircraft X descending to FL320. Now I have two planes in conflict that are both descending. I went back and asked the Aircraft Y to climb back up to FL340. I see the Aircraft X start to descend out of FL340 then he returns to FL340. Aircraft X does eventually descend to FL320 and loss of separation was avoided. I jumped on the landline and shouted out to ZJX to switch the Aircraft X. At that point he was 20 miles inside my airspace and ZJX hadn't switched him yet. I believe that traffic volume and unusual traffic flow contributed to this situation.The sector above me had it even worse than I did. ZJX had stopped taking many of his hand offs. Hampton was forced to spin multiple aircraft. They also were continuously fed the stream of aircraft that would have normally been flying down the east coast and have never entered their air space.I think the important thing to realize is that no notice holding that was occurring in the sector above me is not uncommon. I personally have on a previous occasion had to spin out 4 aircraft all going to different airports because ZJX refused to take the hand offs. I vectored them around in a red (very busy) sector while we figured out what ZJX wanted us to do them. Apparently they wanted them on different routes outside of their airspace.The FAA needs to do a better job of being aware of triggers that could lead us into similar situations. I believe that ZJX should have been 'ATC alert staffing trigger'. I have heard from multiple sources that ZJX was under staffed. Coworkers stated that J34/J33 were down to 4 controllers when they should have had 8. It was also stated that they were pushing 4 hours on position. If this true they should have been ATC alert staffing trigger. To my knowledge the alert was never issued. Had the alert been issued then perhaps the traffic flow could have been reduced to alleviate the stress on the controllers. Instead what happened is that we attempted to dump many extra planes into J34/J34 and the sectors that could not handle the volume.Even if sectors J33 and J34 had extra staffing they have no way to split the sectors into a high and ultra high. It is my opinion that they should divide the airspace. Instead of owning FL240-FL600 it should be divided so they can split off FL240-FL340 and FL350-FL600. They need a high and ultra high sector. That way when volume picks they can manage a greater number of aircraft. It will be a safer operation because you will minimize the number of planes a controller has to watch. This will allow for increased focus and attention on individual flights. This is especially important in unusual situations like this one or when weather is impacting their sectors. They also won't be as quickly overwhelmed.Another suggestion is to create an ATC alert weather trigger to our current list of potential triggers. To my knowledge this is not a current option. Clearly in this situation planes needed to be routed around the weather. The problem is that we were funneling 2 sectors worth of traffic into one sector. It was clearly to much volume for the airspace. We were operating above max capacity. These sectors were not designed for this flow/routes or volume. Perhaps had there been a 'ATC alert weather trigger' in the impacted sector some of this could have been avoided. It would have gotten attention sooner instead of last minute reaction and knee jerk decisions. Prior planning would have been extremely helpful in this situation.I can think of other instances on different days when ZJX shut the door and put us in no notice holding. I think if they are getting overwhelmed the sooner they let us know the better. We can begin formulating a plan and maybe start slowing down the aircraft. We could potentially start spacing out planes. The problem is when they shut the door we are typically already busy and then we are crazy busy spinning aircraft.This trend of holding aircraft continued into the evening shift. I really hope someone looks at the big picture and traffic flow on date. This problem didn't just affect my area and ZJX. The back up was in other ZTL sectors and other facilities. I'm not sure if you are aware of this but ZTL; ZJX and NATCA all were mentioned on news. They were referencing the flight delays and staffing shortages. This is getting national attention outside of the agency.I have to say this was extremely stressful situation. It took its toll on me and my co-workers. I imagine it created stress in the cockpit and on the flying public. We have to do better. We need to find ways to keep situations like this to minimum. It is my hope that we work together to come up with some solutions. When situations like this come up again that we can have a plan to help mitigate the effects on passengers; controllers and pilots.