Monday morning tactics blues...

Usually I do tactics puzzles only on work days and use the longer time slots during weekends for things such as going over an annotated master game. When I restart my tactics efforts on Mondays, it often feels like starting from scratch again - I fail to see the most obvious pattern and everything takes so much longer than it did on the previous Friday. Can one really loose significant board vision by skipping puzzles for only two days??? Or is it just because I should have gone to bed earlier Sunday night? Anyway, I have to get back to the tactics puzzles because I won't give up that easy!