It was the middle of the night and I woke up due to some disturbance. After waking up, I realised it was midnight, but what had bothered me to wake up?

I was quite unsure, as I was woken up from a deep sleep. I sat on my bed wondering what disturbed me. I couldn't figure it out and lay down. Something was moving under my mattress on the bed, and I could feel it. I touched my bed and felt some lumpy texture under my mattress, but I didn't understand anything. I thought to check that the other morning and went back to sleep.

I felt some light in my eyes, and I woke up and realised the night was over. It was the other day. I couldn't move myself. I realised something held me tightly and tried to present its texture. I tried to move myself and realised it was slimy. The slimy creature had grown the whole night and came out from my mattress on the bed. It showed itself to me that I screamed in terror and still felt paralyzed for a few moments. It all disappeared like it would come back again, very soon.