A thought - what if you focused on deriving your sense of satisfaction with your level of present effort, as opposed to the result?
I run into a somewhat similar situation as yours with practicing music. I know when I've played really well, and it's painfully obvious to me when I've slipped a bit. But of course, the reason for my frustration is because I have a memory of playing better, and that memory invades my present perceptions. However, if I ask myself "Am I doing my best now, right now, given my circumstances, energy level, etc.?" - and I make that question the measure of my experience, I can feel very satisfied and encouraged, even if I'm not "objectively" playing as well as had previously.