Hi Tosh, tiredness, yes I suffered from this a couple of times since diagnosis. Before diagnosis if I sat on the sofa I was always out like a light. I find I get it when I relax and it always seems to be coupled with (for me) needing to wee and feeling cold and at the time my bloods were always in the 5s! This sounds like the same symptoms as you. I used to shake myself out of it with a cycle but don't know if that is sensible. I read recently this is possibly caused by your body being in a state of mild shock.
This, to me, makes sense. You are changing your life style: eating less, changing what you eat, doing more exercise, glucose levels dropping all the time. The poor thing thinks you are in imminent danger and is trying to shut down parts of your body to keep you alive. I have read that even drinking too much can cause this (who would have thought).
However, you read such rubbish on the internet some times so who knows it could be a load of (insert you favourite ending here) ______