Returning from a 1 hour break

so I've just ducked out for 2 hours to inspect a house. all great.

now i'm back and looking at the same study i feel as though i've completely lost ability.

usually i start with a collection of warm up exercises.
- fischer.
- sevcik.
- schradieck.
- wohlfahrt.
- kayser.
- ...

The strange thing is. If I get confident with anything in that collection and then return directly to it, without all the preceeding warmup, it's as though I've lost some ability.

WHY IS IT DIFFICULT TO RETURN TO A PARTICULAR STUDY?
WHY IS A WARM UP SO DISTINCTLY IMPORTANT?

It's as though if i warm up the particular skill for a given study i achieve nothing. I've i do a few scales it doesn't help. It's as though I need to do the entier work through of a collection of things.

Alternatively, perhaps it is a timing thing. Perhaps i simply need to be playing of 30 minutes, something simple and analytical, maybe that will do the job. Perhaps warming up requires more patience??!

Perhaps warming up requires.
- more time than expected.
- more breaks along the way to ensure no stress.
- a variety of exercises.

... this all sounds like a very impractical source of entertainment :(

It's as though all violin practice is a warm up which is simply lost in the wind within an hour.

Perhaps all violin playing *is* simply a warmup. Perhaps the warm up never ends?

How to perform or playin a concert without a warm up? Why is this all so precious?! I'm sure people play well without having had a warm up...?