It is highly unlikely that a person ever swallows a spider while sleeping.

It is a common belief that people swallow about eight spiders a year. There
is, however, no evidence for this myth. It is highly unlikely a spider
would approach a sleeping person, and more unlikely that the eight-legged
arthropod would enter an open mouth. The vibrations caused by breathing,
moving and snoring during sleep repel spiders. Hence, it is highly unlikely
the average person swallows even a single spider while sleeping. The
chances are even lower for those who sleep with their mouths closed.