At least on piano, you can snack during rests… my sax doesn’t take kindly to eating while playing. :)
Maybe get some cheese and crackers, and when you start to feel cold (or notice other symptoms), eat a bit? (might leave out the crackers if you don’t want crumbs on the keys)
Maybe take a 10 minute break to just breathe and look out the window?
Some meditation to relax might help – maybe some listening exercises with your eyes closed? Just ‘feel’ the music instead of dissecting the theory of it?
That might help you reset your fingers and let them soak in the practice, too… so your next run through is “fresh”?
What type of music are you playing? (I do swing/jazz on sax – but just as an amateur)