I dreamed that I spit out a dead mouse from my mouth. That's disgusting. What does this portend?

Generally speaking, there are two possibilities to have such a dream:

Psychologically, this dream shows that you have something on your mind recently, but you can't say it for some reason;

Physiologically, there will be tinnitus, dizziness, or back pain and weakness in the near future;

Therefore, pay attention to psychological adjustment and strengthen exercise, and you will be fine. There are no other signs.