Your nose is connected to your eyes, your throat and your ears by way of ducts, to allow secretions to drain naturally.
Sometime things get clogged up and "back flow".

Hence the "sleep dust" as we so politely call it here.
If it gets to be a big problem, a trip to an Ear, Nose and Throat specialist (see the connection?) may be necessary. To clean the ducts out.
Cheers
Mick