EMB ERJ 175 Flight Attendant reported the forward lavatory smoke detector activated. The deadheading Flight Attendant assisted in the troubleshooting and assisting a passenger with a medical issue.

Narrative

I was dead heading sitting in seat XA dozing off and on. I heard some chimes that were not normal chimes and then I heard the Captain (CA) call on intercom line. I looked up and noticed the forward lav smoke detector was going off and the B Flight Attendant (FA) was talking to the CA.A passenger came out of the LAV. I waited/watched from my seat for a minute or so. I was thinking the passenger was vaping.The smoke alarm did not stop and I saw the FA's checking the LAV for any smoke or fire.The alarm sounded longer than it should have for a passenger vaping and I thought it was odd. I believe the FA's had checked the LAV as they should have and could find nothing alarming and had closed the LAV door. The detector alarm was still going. I decided to go check the aft LAV just as a precaution; since it was strange the alarm was still activated. I walked to the aft galley and just looked in the aft LAV. It was fine.The CA called on the intercom line and the B FA answered and I picked up the aft phone so I could be aware of what was happening. CA asked if the passenger and been smoking; B FA asked her. She said no and then I asked if she had been vaping. B FA asked her and she said no. CA said he'd call back. A few moments later he made a PA and said we would be landing in ZZZ and there didn't seem to be an issue (not exact words). Detector still going off..At that point; I was still in the aft galley and I noticed a strange order. I asked 2 passengers if they could smell something odd and they said yes. I made my way to the forward galley; stopping half way to discreetly ask another passenger if he could smell something odd. He said yes. That it smelled 'Fumey' it was a perfect description since I couldn't put my finger on the smell. It wasn't gas or oil smelling but some kind of fume odor.CA called on intercom line again and I went to the forward galley to let them know I could smell something odd. I asked B FA if she could smell something. She said yes. I told her she needed to tell the CA and she did. I did not hear what he said to her and they hung up. Nothing seemed to be wrong in the forward LAV and both FA's were there; so I walked back to the aft. I wanted to make sure the odor wasn't getting stronger in the aircraft.B FA collected trash and came to the aft where I was standing. The alarm did stop at some point; but I can't exactly say when.The CA called the intercom line again. B answered and hung up and told me we were landing. I assumed in ZZZ; since the CA had just made that PA. I decided to head back to my seat so the FAs could prepare the cabin. As I was walking to get to my seat; I noticed a woman having an anxiety attack. Several passengers were talking to her. I stopped and asked if she was ok as she was trying to catch her breath. She told me she was having a panic attack. I made sure she had a sick bag and turned on the gasper valves. Passenger told me he was a DR. I informed him I was going to go get her some ice and a larger bag in case she vomited. I went to AFT galley and told the B FA we had a medical situation and I needed to get ice and a bag. I walked back to the passenger and checked on her. I asked the DR and a passenger to switch seats so he could be buckled and available to help her if needed. I also asked a passenger in seat to move to A and I took his seat in front of the women having the attack so I could monitor the situation. I let them know we'd be on the ground soon. Neither FA offered any assistance or was very visible in the cabin. I do not believe the A FA was monitoring the forward galley for any further issues. I do not remember if they did or didn't prepare the cabin. After a minute or so; I asked the passenger in seat A next to me to open the window so I could see how close we were to landing. We were very close to landing and clearly it wasn't ZZZ. I did not see the FA's again and neither offered assistance or acknowledged we had a medicalissue. I looked at the forward jumpseat to make sure everyone was ready to land. The A FA was not there. I turned to see if she was in the AFT galley or on her way up. I could not see either FA. Imminent landing chimes went off and still no FA. I thought maybe A FA was having an issue and couldn't take her jumpseat. I quickly went to the back to see if she was ok and if needed; I would take the A jumpseat for landing. When I walked back; B was in her jumpseat and the A FA was sitting in the 3rd jumpseat with her earbuds in. I told them we were ready to land. She took her earbud out. I proceeded to tell her she needed to get to her jumpseat or I would. Neither of them seemed to have any situational awareness or clue that we were landing at any minute. (And that it was urgent) I went back to my seat. A FA got in her seat less than a minute from landing. We landed and went to a gate. I was completely unaware that we were and had in fact diverted to ZZZ1. The passenger having the medical; was crying but ok and the doctor said he'd stay with her if needed. I thanked him and we deplaned. I spoke with CA to describe the odor smell and he told me they could smell it in the cockpit as well. I did speak with the A FA and she mentioned that she smelled something during takeoff but didn't think anything of it. I told her she should have at least mentioned that to the CA.