I have felt exactly the same over the last few months. I have fallen asleep at work and in meetings and I'm far too young to be the person that does that!

I have learnt a bit about CBT which is about the fact that how you think is how you feel and how you feel is how you behave, and how you behave effects how you think. My counsellor said the key is to do stuff even if you really don't want to because it will help break that cycle. This has definitely helped me.