M20 pilot reported a loss of aircraft control and deviation from assigned altitude due to severe turbulence.

Narrative

I departed ZZZ approximately XA00 hours [on] Day 0 on an IFR flight plan to ZZZ1. After departure; my primary flight instrument (artificial horizon) failed. I returned to ZZZ without incident. After troubleshooting the problem on the ground; I made a decision to fly back to my home base ZZZ2 singly backup instruments (Aspen Pro). I departed ZZZ at approximately XB00 hours. Climb out was without incident. Upon reaching my assigned altitude; I encountered severe turbulence. An updraft shot me up approximately 1000 ft. within seconds and then a downdraft shot me down just as fast. The severe turbulence accelerated upwards and downwards getting me into an unusual attitude. I was finally able to regain control; busting my assigned altitude higher and lower. The remainder of the flight was without incident.I think flying on backup instruments (which I was not accustom to) and encountering turbulence in IMC lead to getting my plane into an unusual attitude. Busting my assigned altitude was directly influenced by the turbulence. I know that more practice using backup instruments is paramount and will be done. I have had instruction on recovering from unusual attitudes during my BFR (Biennial Flight Review) over the years; but never in severe turbulence. I think and plan to seek this type of instruction in a flight simulator. Taking corrective action in turbulence is completely different than in smooth air.