Does any body know why eating makes my energy crash at midday? As soon as I've eaten lunch I just have to take to bed and sleep for the rest of the day. Eating makes me unbelievably exhausted. I can almost feel my heart slowing down, it feels like eating makes it struggle to keep going. My basal pulse is 59 - 60 at the moment and basal temperature is between 35.5 and 36.5 so my metabolism is very slow at the moment. I was only diagnosed two weeks ago with under active thyroid. Does anyone else have extreme exhaustion after eating?