Ulcerative colitis causes several problems that can make you feel very tired:
Nausea and loss of appetite keeps you from eating, which leaves your body low on fuel.
Diarrhea and swelling in your colon make it hard for your body to absorb what it needs for energy.
Bleeding in your colon leaves you with too few red blood cells, or anemia.
You don't get enough sleep because you get up often at night to go to the bathroom.
You're dehydrated because of diarrhea.