Of course, it's only natural that you 'lose it' after a long dry spell - be it playing guitar, sex or any skill-intensive activity .. (did I say sex?
)
First on the blame list are physical factors, I guess ("my fingers are stiff", "gee, I must be slowing down with age", "pasmado ako eh ... etc, etc.) While these may be valid up to a certain point, I don't think they're enough to take the brunt of your excuses.
For the most part, I think the 'losing it' syndrome is mostly psychological in nature. Maybe you're just not inspired enough to play. Maybe you're feeling frustrated that your friends are making so much progress and sounding great while you're not. Maybe you're just too saddled with the realities of everyday life that you can't just spend as much time playing (even if you sincerely want to).
Maybe part of it is because you're just trying 'too hard' to play better, to the point that your just bombarding yourself with too many 'shoulds' (i.e. "Steve Vai says I should do this ..", "Eric Johnson says I should use circular picking") which in the end do nothing but confuse you.
There is such a thing as 'information overload,' after all ...
What you can do ... is just play for the sake of enjoying your playing. That means that you can just indulge yourself and play IN THE MOMENT - without any fear of 'doing the right thing'
I believe that it is during these moments of reckless abandon when your 'inner self' emerges - your natural, child-like self who isn't afraid to make mistakes or to challenge the status quo.
Contrary to what psychic_sushi said about lifting weights though, I don't quite subscribe to the belief that lifting weights will 'slow down' or affect your playing. I dunno, it just hasn't done so for me ... On the contrary, I think judicious workouts should strengthen the very same muscles involved in playing. But then again, that's just my two cents in that regard..
Finally, it always helps to keep yourself motivated to always play your best. There's nothing like having a set of player-friends who you can always jam with and give you constructive criticism..
Hope that helped ..
Oh, by the way, we're not 'masters' by any chance ..