Maybe your playing isn't changing at all, but your expectations change dramatically when hearing other people play? Perhaps while you think your critical listening skills haven't changed... they have? (I couldn't find a nicer way of wording that, so I'm very sorry in advance)
The thing is, there are definitely times when I think I'm playing great, then I hear other people and realize I'm not. And there are lots of times when I hear new things from recordings I've already listened to, to death. I know my ability to hear hasn't improved or deteriorated, but my perception does change.
Someone has said a few times around these boards that periodic visits to "the well" are needed to refresh one's playing. I think that's true for most people. Maybe you need to go play with great players *now* while you're in the trough?
For what it's worth, when I go to weekend things like that, I usually find my playing improved. I often suffer post-festival let down and stop playing for a few days, but during the event it's just more and more fun... usually anyway. So maybe we're too different for my advice or insight to be accurate.
Lots of interesting stuff in there, Nico. And you don't have to worry about offending. I wasn't at all bothered about the comparison between my playing and other people's. As it happens (sorry anybody who's reading - I don't mean it nastily), I didn't think all that much of most of the playing at that weekend. It was kind of OK. Some was fine, and some was not so fine, and most was in between. No, it was just my own playing, being, to me, suck-worthy, that bothered me.
Go play with great players? Now, there's a thought. I'd know where to go. But I can't get there just now. There is one fella whose playing might help ... hmmm ...
I have worked something out - when I go to a festival, or some such, my playing does at least stay at the same level, or even improve. But there is one small difference that maybe makes a big difference to my playing. Whenever I'm at those things, I find a way too have, say, 10 minutes playing by myself some time during the day. But at this thing, that wasn't possible. I was staying at an ordinary hotel, and I just didn't find an opportunity for that private time. I think that might have made a big difference.