Acid Reflux while sleeping...
Make an appt to see your doctor and get some saline out. You don't give us much information but I am assuming you are not newly banded? It is not uncommon for scar tissue to build up after a few years and cause the band to feel tighter.
It has happened to me twice, once at around 4 or 5 years and once at about 7 years. Both times I had a tiny amount removed (just 0.1 ml) and that sorted it out for me. My reflux was night-time only but less severe than yours. But as it is not during the day and not related to means, this may well be your problem.
Don't leave it. Night time reflux can be dangerous. It can damage sensitive tissue, lead to oesophageal problems and even to pneumonia if you inhale the acid.
Highest 290, Banded - 248 Lowest 139 (too thin!). Comfort zone 155-165.
Happily banded since May 2006. Regain of 28lbs 2013-14. ALL GONE!
But some has returned! Up to 175, argh! Off we go again,