Thanks for all the responses so far. I never thought it might be a hallucination. I have struggled with anxiety for some time and struggle to sleep well but I'm doing better lately than I have in a while. I'm losing sleep but far less than I have for several years. If it continues, maybe I'll get checked out.

I had a similar problem once. Problem was the smell wouldn't go away (it was like a sweet campfire). Oddly enough the cause was infected root in a tooth. I was told sometimes this manifests itself as pain but once in a while it becomes a smell.

I tell folks about hypnagogic hallucinations regularly over in "Insomniacs" [healthline.com]

[mayoclinic.org]

It's almost certainly nothing to worry about, but it might be worth getting that checked out by a doctor. A friend of mine began experiencing olfactory hallucinations in his mid-20s, regularly smelling food when there was none around, which he initially thought was something to do with him being a chef. However, he began to experience it more and more often and eventually spoke to a doctor about it and following tests was diagnosed with early-onset Parkinson's Disease.

early start to cooking by a neighbour?

Happens