Aqua

I was swimming in an indoor swimming pool and there were these mermaid-like creatures swimming at the other end of the pool. One of them swam over to me and pointed at my arm, "Vat tis vrong vith your skin?"

I looked down at my arm and noticed that it was covered in tiny blue and purple dots. "Uh..." I replied and the creature lunged at me and I got out of the pool and ran out the door that leads outside. It was nighttime and the only light was coming from a partially open door at the far end of the building.

I walked slowly towards the door and peeked inside. The room was empty except for a few boxes stacked on top of each other in the corner. I put one foot inside and EXTREMELY LOUD music started playing and I was so shocked I woke up.