Similar to sleep paralysis by description. It does not depend on stress, fatigue. Many people see balls of thread, spiders, sometimes even snakes, or feel something pressing on their chest. At first it is very scary, but then you get used to it. This is not dangerous. The causes of sleep paralysis can be read on the Internet, there are a lot of theories. No one for certain understands the reasons for its occurrence. There are only guesses. It is recommended to fall asleep in certain positions to reduce the risk of these hallucinations.
Eugene, no one is sure to answer your question by correspondence. But the subconscious usually represents your ambitions in the form of a spider. Maybe you shouldn't drive yourself into such stress just because you want to be the best?