I read somewhere that the ideal nap window is 20 to 30 minutes, but that never worked for me. Turns out my sleep cycle takes about 40 minutes to dip into deep sleep, so I was always waking up mid-cycle and feeling worse. Found a sleep study from UC Berkeley that said 60 to 90 minutes is better for most adults, and I tried it last Tuesday. Now I'm curious, does anyone else use the longer window or do you stick to the short one and just deal with the grogginess?