Should you eat first thing in the morning?
Generally, you should not eat first in the morning, especially when you haven't had a good full night's rest. This is because your body is just waking up and eating something first thing when you get up can literally shock your system.
It's best to give your body some time to acclimate to the day and let it "break in" rather than eating first thing when you get up. Eating just when you get up is especially worse when you've had a poor night's sleep because your body's digestive system did not have a good long time to rest, recover, and rejuvenate from the previous day's eating. So usually digestion will be very poor if you eat just when you get up from a bad night's rest.
The best thing to do in the morning is usually just drink water, which requires literally no digestive effort from your body, or just wait a few hours for your body to "break" into the day and then eat something. Digestion then at this point will be a lot better and your body can assimilate food better.
If you look at it common sense wise, this information does make sense. I hope you find success with it.