Why am I dying when I go outside?

I admittedly haven't played Oblivion in a while and may have forgotten something as whenever I go outside, my player starts losing health. I know this wasn't happening to my player before stopping playing.

I completed a mission in a dungeon from my last save, head outside, and my health slowly depletes until I'm dead. I can't fast travel anywhere because of it, and healing potions only delay it.

1. What should I look for?
2. Can it be fixed?

If it matters, I'm playing the Xbox 360 version.

Solution 1:

It's most likely that your character is a vampire. There's a quest you can complete, found on the wiki, that will cure this. It's also possible to cure it using the console. Other than that, you can avoid damage by staying out of the sun, and fast traveling at night.

Solution 2:

You have vampirism.

An easy way to get rid of it: Theres a glitch. First go into the water then drown. After you're dead, load your last save and vampirism will vanish, but not permanently. Maybe the next month you'll get vampireism.