I Have Extreme Fatigue Before A Bowel Movement At Times.

I have extreme fatigue before a bowel movement at times. Its almost as if I am being drugged or knocked out. I fight it until I can't anymore or until the BM happens. Usually I have to take a quick 20-30 minute nap and when I wake up my body is ready but prior to my nap I can't go. I have no idea what I need to be eating differently to stop this because this happens even when I am consuming mostly a plant based diet as well.