Though guitar uses fine motor skills, there are repetetive stress things to watch out for. If you start feeling any tingling or sharp shooting pains in your fingers, hands, wrists, forearms, etc., stop...don't play through it.

When you get fatigued, your form will go to pot and you will start compensating. I would back off if you notice this too. Just like in any physical activity, pushing through this can lead to injury. It's also inefficient.

It sounds to me like you have a nice variety of what you are doing throughout the day, and you are taking breaks. I belive those two things are very important. I've experienced what Christopher is talking about where your body and mind need down time to absorb all that you are doing. I've gone to bed after struggling with something and woke up the next day able to fly through it.

Breaks are important and remember...slow and steady wins the race.