When I first got my PCS I realised I needed to rest, and thought 'hey this is a good opportunity to do a load of reading on medical issues for work that I've been meaning to do for a while' and sat out in my garden reading very complicated books for a week, in between watching action films and playing computer games.

This is not cognitive rest! I didn't understand the difference between cognitive and physical rest, and that there are things that can work your brain very hard while your body is at rest. In my experience things which tire out your brain are

(a) anything that is complex for it to understand (like complex medical textbooks I was reading)

(b) anything that requires it to keep track of lots of different things at the same time or quickly switch attention from one thing to another - this would include most fast-moving console computer games, situations where you have to try to, say talk to someone whilst your brain is also listeniing to other conversations or the tv in the background

(c) anything which puts pressure on your brain to respond quickly, eg people asking things of you in a demanding way (I get this a lot at work) or action films/music videos etc which are designed to keep changing scenes and hitting you with loud noise and bright colours so your brain is constantly having to reorientate and pay attention.

C is the biggy for me since my brain will tend to rise to the challenge whether I want it to or not, my processing speeds up and I am able to cope with the demands being made of me.... but then the effort brings my symptoms back afterwards. I work in mental health with a lot of desperate people and I have had to work periods without patient contact because my brain couldn't cope with all the demanding requests they kept making of me.

Lying in a dark room all day free of stimuli may well be helpful and if you are able to do it by all means give it a try. Personally I'm not capable of doing that as the boredom would drive me insane - instead I have tried to do things which interest me, but which don't make too many demands of my brain. These include watching nature or certain types of history programmes, reading books which aren't too difficult to understand and when I felt a bit better going to watch a quiet game of cricket or visiting a historic site where there aren't too many people around. It depends on what you're interested in and what your brain can tolerate, but if your symptoms get worse afterwards that will mean it was too much.