Would a native help me correct these sentences please?

Could a native help me correct these sentences please

I'm not sure how to naturally say this?

1 I'm the person who stays mad the least amount of time. I'm mad one second, and the next I'm not.

If there is a big mess and you clean up most of it, little/ small mess to do. Which adjectives to use and naturally say it?

2 I cleaned up the biggest part. We only have a little mess left to clean up, the biggest part is done.

How do you say the last part " have something worse than you actually do" or "sickness is worse than it is" how to say it?

3 If you don't tell him what's wrong with you, he might think you have something worse than you actually do. (sickness)

Thank you so much