Olfactory hallucinations, yes. Mine started 20 years ago. They don't last terribly long, and fortunately they're not frequent, because they've always been the exact same smell: rotten chicken(!) Yuck. There's no chicken, rhyme or reason to it. Definitely hallucinations. Yet so realistic.

Interesting timing, your question, because just this week I've been smelling gasoline. Multiple times a day. BF can't smell it. There's no gas. Today I had an idea, and am testing it, hoping for an alternative explanation.

Each time they've happened awaking you from sleep? I've awoken from the chicken smell, but it also happens at all different kinds of times.