Given that you are in California, I'm tempted to ask why you are keeping what should be an outdoor bonsai indoors! Insufficient light an overwatering are the obvious problems, possibly made worse by being chilled by air conditioning - You might find http://www.bonsaiboy.com/catalog/fujicare.html helpful - it's written from a New York point of view but includes some temperatures that might be useful guidelines.
Good luck with it.

The reasons are as stated in my post: I would certainly keep it in full sun, but I don't have a full sun location at my disposal. Given that it has been unusually cold, I would need to keep it indoors anyway, per the instructions you provided. So I guess I'll need to find a full sun location!
Thanks for the feedback and the resource!

Can't me much help, but just wanted to admire it. As a last resort perhaps one of those artificial dalight lamps might help?

It's not a Serissa, anyways, but a Chinese Elm, and it definitely needs more light. A gooseneck lamp with a high-wattage, full spectrum, compact fluorescent bulb would do it good.

I thought it didn't look like a cherry. Isn't a Chinese elm deciduous or semi deciduous anyway?

I'd echo the full spectrum lamp or one that has more in the red/blue ends as these are the wavelengths the plant uses. Tubes sold for aquariums usually have the correct plant spectrum. Normal tubes are too much in the yellow range.

The small-leaved forms used for bonsai--'Catlin' and its kin--are normally evergreen, except in pretty severe frost.

I am just seeing these replies, sorry! Is it really not a Serissa?! I was given as a gift but it had this tag on it!! So a Chinese elm huh? Thanks for the great wisdom!

You're welcome! :)