“Bed bugs have survived for many years by being elusive. Hiding is what they do best. In fact, their main defense mechanism is to only come out to feed when humans are unlikely to be aware of them.
Bed bugs are nocturnal, so they tend do to come out at night. They come out whenever they think they can get a meal safely and that’s usually when their hosts (us) are sleeping.
Basically, they crawl onto your body when you won’t notice them. You may not be asleep when they crawl on you. It could be when you’re at school in class, at work when you’re sitting in your office chair or when you’re relaxing on the couch.
Bed bugs are very small, especially during the nymph stage. They’re only about the size of a grain of an apple seed or a lentil. Therefore, it is extremely unlikely to feel when bed bugs are crawling on you.
Additionally, you will not feel it when a bed bug is biting you, because while biting you and feeding, a bed bug injects saliva that contains an anesthetic (a numbing chemical) and an anti-clotting agent so your blood with flow freely. You likely won’t feel a thing.”
Courtesy of: The Bed Bug Experts