They can get frustrated and bored if they're outdoor cats and they're stuck
in the house due to winter.  Also if it is gloomy and cloudy for days they
seem more lethargic.  Mine seem much happier in the winter when the sun
finally comes out; they come to life, start running around and seem happier,
so yes, I think animals are affected by weather.  

Cat aroma therapy?  All I can think of is catnip.  Also try playing with them
more in the winter and try out new toys - mine love a piece of tissue paper
on the floor; I put a toy I have (Tail Chasers Series - I got the Cat-apult
and the Rabbit) underneath the paper and swish it around;   .  They go nuts
when they see the long tail under the paper.  For some reason, they love
playing on tissue paper more than just the bare floor - maybe the sound?  

Here's the link for those toys but I just got mine at the pet store:

http://www.fatcats.com/html_site/cats.shtml

Anna