Hrm ... no idea.

I'm assuming your in bed and then you wake up. It could be:
-bed bugs
-allergy to dust/ dust mites in your mattress/ bedding
-allergy to down/ feathers (if you have these)
-allergy to the detergent with which you was your bedding

I would suggest getting it checked out by a doctor to get a diagnosis if it persists.

I have a rash that happens mostly in the middle of the night it starts to itch and then when I scratch it gets really swollen, what is that?