Heightened sense of smell?

If I wake up early in the morning, around six (usually for school) I've noticed i have a super-strong sense of smell. Like I open the fridge I can smell all of the food and stuff. And when when I open the cabinet doors (it's basically a pantry), I can barley handle the smell from the strength. Or this morning when I put brown sugar in my oatmeal, i smelled it very strongly. It usually take 15 minutes to wear off. Why do I get this?