The assumption that someone may swallow a spider while sleeping has almost become an urban legend or myth. But, is it real?
Facts show that spiders do climb onto the beds when hunting at night while humans are sleeping. They go in search for insects but, of course, not humans. Yet, spiders bite humans in their sleep, because people tend to move while sleeping and roll onto them (learn more in Why spiders bite while humans are sleeping?). Now, spiders do hide in small dark places, especially holes, and a mouth wide open of a person sleeping in his bed just appears to be a good place to hide. Even though this is partly true, there are some details that should be taken into consideration. First of all, we are breathing. This means hot air going in and out from our mouth, and spiders know --in the way spiders are able to know-- that such a hole is not a safe place. There is also another thing: despite the fact that a person can be asleep, the inside of a mouth is quite sensitive, and anything with legs crawling into our tongue will be enough to wake us up. Even if the person does not wake up, he will probably push back the spider with his tongue, close the mouth immediately when something is over his face or take it off with a sleepy hand.
So, are there any chances of eating a spider while being asleep? Unless you are very hungry, these are REALLY LOW.