In answer to the question is there such a thing as practice fatigue, I think there can be. Maybe two kinds. One is when you're tired or get tired during practice and start messing up. might be just as well to pack it in instead of "practicing" bad technique. The other is when you get burned out, maybe just trying too hard or making every trip to the range too intense/too long, etc. Not having fun. It's hard to fit practice in when you have family and work and other things to do, so much (maybe all?)of the time you have for recreation and relaxation is being spent in that practice. Everybody has the challenge of balancing everything and it's possible to get worn out.