Slightly swollen since we moved to the mountains, and she likes to sleep under covers.
She is born and lived for 14 years at sea level, now she is at 1500 meters ( 700feet) in altitude. She also is on medication for hyperthyroidism since 4 months.
What could this swelling well be?

It could be many things, an infection, irritation and many, many other things.

The best thing to do is go to the vet.

I know that in humans hyperthyroidism often causes the eyes to bulge.
Perhaps it is that or it could be an allergy to something in the new environment.
A vet is always your best bet!

I know that in humans hyperthyroidism often causes the eyes to bulge.
Perhaps it is that or it could be an allergy to something in the new environment.
A vet is always your best bet!

Thanks a bunch for your kind words; will go to the vet with my luv'ly cat
2savvy