Dreams.

so I just pulled the blanket over my head so I wouldn't have to see it

That's a perfectly reasonable reaction to nighttime hallucinations.
Revan, why are you afraid of spiders? Spiders are cute... As a child, I occasionally had dreams about spiders in a negative light. Once, I dreamed of a giant harvestman spider that was bigger than the house, and it was creepy. Another time, there was some strange spider on the bed, and I tried to swat it with my hand, but it wouldn't die and became noticeably bigger after each attempt, so in the end, I was like, "Ugh, it's already the size of a dog, time to get out of here!"
But lately, it's been the opposite. You walk past a wall, and there's this cute, fluffy black and white spider sitting on it. And I stood there for a long time, admiring it... It's a good thing no one saw me.