When I had Covid in March '20, I lost all taste and smell for a week. For another week or two it gradually came back, but heavily shifted towards stale cheese/ coffee/ smelly feet/ rotting onions mixed with something metallic.
It eventually got back to normal.
Then in early July '20, I felt run down and that smell sensation returned, but only slighty, and only noticably on certain scents - urine, particularly the first wee of the day, cat food, and very very slightly on some cold meats in sandwiches. And it's been like that since, i've just got used to it as the new normal.
Until this morning, waking up with a headache/ run down feelings post - 2nd vax, I went for a wee, got a half second strong burst of the stale cheese/coffee etc scent, then... normal, pre- March '20 wee smell.
I don't know what to make of it.
I also had, last March while my sense of smell was slowly returning to normal, strange little bursts of scent, particularly as I was going to sleep - a half second of strawberry, or freshly cut grass...