Hey, sorry to hear your troubles. My brother-in-law was told the same thing and that he'd have to have surgery soon for gall stones. He went home that day and my sis put him on a cleanse. He drank all the apple juice he could stand (and then some) for 3 days along with other liquids, but mostly apple juice. On the third day in the afternoon he drank 1/4 cup of olive oil and 1/2 cup of lemon juice. (Stay close to bathroom) He passed all the sludge and gall stones and no longer has trouble with gall bladder. This is an old remedy from Back to Eden natural cures. You never know!! But I always say "do the research". Hope everything comes out ok.
Weight loss is one risk factor for cholecystitis. So is being overweight, being a woman, heredity, and others. My surgeon's gallbladder went all of a sudden, and he didn't have stones. But his gallbladder became gangrenous within hours of the onset of pain, which is scary.
You can talk to your doc about using some meds to try to dissolve the sludge. It may or may not work, and you may or may not be a candidate for the meds.
If you lost weight very rapidly it's possible the condensation of your bile may have been pushed toward 'sludge' formation.
The sludge may or may not cause problems other than nausea. It's something you should fully discuss with you doc. Many docs will suggest removal of the gallbladder if the sludge exits the GB and enters and irritates the common bile duct. That could cause a lot of problems.
While you're trying to figure out what you're going to do, you may want to make sure you keep yourself well hydrated and follow a low fat diet.