anyone experience this?

i'm not sure if it's bodybuilding or if i'm just bad at having too much going on at once. i've been doing short 20 min workouts because if I go to exhaustion, I go into a "rest mode" for like 2-3 hours after a work out. short cardio workouts pep me up, but heavy volume bodybuilding workouts are like a sledge hammer to my brain and i just feel "dead" for a few hours afterward.

i'm not trying to make excuses to get out of shape because i am doing cardio + *some* resistance work, but i'm not able to lift heavy + with a lot of focus anymore because it messes up my brain.

anyone else experiencing this?