Running in my sleep

I've been feeling tired recently. Running has been hard. I'm not getting puffed out but my legs are tired. I am tired. I can sleep for England. I can sleep for the USA too. If pushed I can be caught napping for Zambia. I don't understand it...I'm fitter than I've ever been in my life, I'm taking my thyroid pills what is the matter with me?

After a day of tests, I discover that my pulse, blood pressure and heart rate are that of someone asleep. Apparently my newly found athleticism has sent my vital signs into freefall. The Doctor reassures me that this is incredible for someone my age - he can hardly believe it. And then he looks at his notes and back at me a few times....
"How old are you?, he asks.
"Forty-one", I reply.
"Oh", he says, "your notes say 50, but you're still in great shape", he backtracks...

And then my thyroid dose is raised and I'm put on mega-ultra-massive doses of calcium which he has discovered is non-existent in my blood.

With luck one pill or the other will keep me awake.