Between the hours of three and five in the morning, when you're in deep REM sleep, is when bed bugs usually bite.
Bed bugs typically do not feed until the hours of three and five in the morning. Generally when we are in that deep REM sleep where we are not moving or rolling around. When we are perfectly still it's easier for the bed bug to come out of hiding and feed. It's also the time where the heat and the carbon dioxide cloud is built up the most so they can find us easier.