I have hypothyroidism from past 18 yrs and i am on medication and in control. now i have acute cholecystitis. is this because of my sluggish thyroid?

Not likely: If your thyroid has been in control for those 18 years, it did not contribute to your gall bladder disease. It's common in other disorders, however or can occur spontaneously.

If under rx: If your thyroid function is chronically low and undertreated that could have an impact through your lipids, but overweight and on ocp's, pregnancy also risk factors.