43-lbs?
I lost 131-lbs in 23 days in the hospital, with acute/severe pancreatitis, back in Mar/Apr 2017.
Tough way to get back to 32” Lee Jeans, from a 36-38”.
I gained 8 lbs. after a week in the hospital without eating. Why? Doctor said it was because they fill you with saline liquid (water) trying to flush out your abdominal cavity to get rid of the inflammation in the gut. And water weighs 8 lbs. a gallon.
The etiology for my acute pancreatitis episodes was initially blamed on my excessive drinking. 99% plus cases are caused by binge drinking alcohol. Less that 1/10th of a percent get it from the side effects of certain heart medications.
Problem was, I didn't drink alcohol. Hadn't for several decades. Doctors didn't believe me at first when I denied I drank at all until they talked to my wife, who confirmed that I didn't drink liquor.
Eventually the cause was narrowed down to a heart medication I was taking. Doctor switched the medication and I've never had it again.
I suspect you are a drinker. And were overweight. All the clues you provided lead to that indication.