You do not say where you live. How cold are your winters? Bay trees can put up with temps down to freezing and a bit below before they need to come indoors. I would keep it outside as long as possible then keep it very cool when it comes in. Try not to keep it in a dry atmosphere. Only water a little and do not feed. Make sure it has as much daylight as you can give it. Put it back out as soon as possible.

It initially sounds like a water issue - either too much or too little but I'm guessing at this point. Depending on how much of the plant is still green, there's at least some hope that it can be saved.

A few questions though ... how big is the bay? Where is it located? I'm guessing it's in a pot - if so, how big a pot and what kind of soil?

probably too much water
I have over wintered bay up north in quite cool conditions, 40's, and left them all but bone dry
just enough to keep the stems from shrivelling, I did kill one in my first try by over watering when cool
luckilly down here in FL they grow all year long with the warm temps

About 10 years ago I purchased a small bay laurel in a 2 inch pot and set it out in our back yard in Houston, Tx. Now this tree is over 12 feet tall. Rather than using a bay leaf in cooking, we clip a twig with up to 6 leaves. We give away plastic bags with lots of leaves to friends. What a luxury...

I'm in Zone 7 and keep mine indoors, near a sunny eastern window when the temps dip below 40 degrees. I try and keep some humidity in the room, either by setting the pot in a saucer with gravel and water (not sitting in the water)or keeping an open container of water nearby. I also cut back on watering the plant during the winter. If the temps increase to 50+ (which it has done this year), I put mine outside for the day.
Good luck!

I live in East Tennessee & every year I bring mine in cause I don't think it could survive our winters. I water it very little & once in awhile clean the leaves (free them from dust & add moisture) we tend to get dry air around here. So far I've had good luck with it.