M20 pilot reported an encounter with heavy rain and severe downdrafts resulted in a temporary loss of control.

Narrative

On IFR flight from ZZZ1 to ZZZ; I was in IFR conditions in clouds & ZZZ ATC cleared me outer marker (ZZZZZ) for ILS XX at ZZZ. I requested vectors for ZZZ ZZZZZ and ZZZ ATC gave me vectors. Flying on vector heading; I encountered heavy rain and severe downdrafts that caused temporary loss of control and severe loss of altitude. I recovered airplane in downward dive about 1500 feet altitude. ZZZ ATC gave me new vectors and requested climb for which I complied but was having difficulty maintaining headings. After new heading in several minutes; I encountered another downdraft upset event and again recovered aircraft. At this time ZZZ ATC recommended I change to RNAV XY; which I was attempting to load in Garmin 175 but was unable to simultaneously comply with ZZZ ATC vectors. After a few minutes ZZZ ATC asked what I wanted to do. I asked for vectors to ILS XX and ZZZ ATC provided them. They vectored me back to the approximate outer marker (ZZZZZ) & I got established on ILS XX and handed over to ZZZ Tower and successfully broke out at 200-300 ft in front of runway and completed successful landing.I was IFR current and IFR instruments dual G5's; Lynx NGT-9000; Garmin GPS 175 & KX-155 ILS had current IFR approvals & databases. In retrospect after the first severe downdraft and heavy rain; I think I had unrecognized spatial disorientation that became worse after second downdraft event. These 2 upset events and spatial disorientation apparently reduced my cognitive abilities. Fortunately; after flying for 4-5 minutes; I improved and was able to execute ZZZ ATC vectors; execute ILS XX approach in IFR conditions and successfully land.I commend ZZZ ATC for their superb assistance. I think I could have avoided the second upset event if I was given few minutes to recover from spatial disorientation in retrospect. Everything happens fast in these conditions but I concentrated on flying the airplane.