I hate it when you really want to get on with writing but everything else in your life means you are just too tired. I find that then, even if I try, my writing is stilted and I have no ideas. I can sit and search in my head for ages, not find it, and then take forever to realise I should really give up and lie down!
It's usually a good point at which to pick up a book instead.
At the moment, it's a really busy end of summer term with lots of events happening right up to the end and at all hours. Roll on summer hols... Isle of Wight here we come!