Welcome. It’s ok to feel scared & nervous. It’s surgery. Food likely is something you depend upon as an emotional support & that is going to change & you will be changing what & how you eat.
Things like how much pain you will experience after surgery is very individual. You may have a lot of gas pain or nine at all (I didn’t after my sleeve) but there are things you can do to help the gas escape your body. You may experience surgical pain for a couple of days or a week but again you’ll have access to pain meds to help. You may have muscular discomfort & struggle to get up & down for a little while or you may have very little at all.
Pre surgical diets differ a lot too. Some are two weeks, some are just a couple of days. Some are all shakes. Others 2 meals shakes & 1 meal protein & vegetables. Mine was keto so … (I have done shake diets before & for a couple of months at a time.) The first challenge to the pre surgical diet is the psychological loss of the crunch & chew comfort of solid food. This can increase your head hunger & cause a lot of emotional turmoil. The second is the withdrawal symptoms (headaches, nausea, tiredness, etc.) from cutting out caffeine & sugar. This usually lasts less than a week.
These things are small & are only a couple of weeks in duration. Nothing when you consider the big picture of your whole life & your health. The surgery is an opportunity to makes big changes but you have to be psychologically & emotionally ready.
Don’t be afraid to seek support from a therapist (one who specialises in bariatric patients & disordered eating are best). A lot of people have found therapy extremely helpful.
Yes, you are on a low calorie restricted diet & eating small portions to begin. Initially it is to support your healing. Then to make you look at the nutritional benefits of what you eat but within a few months you’ll be eating more & a greater variety of food. By maintenance you’ll be eating the portion sizes we all should be eating (not those giant plates two & three times more than what we actually need & lead to our obesity). And you’ll be consuming only the calories your body needs to function effectively & maintain your weight. You’ll discover your relationship with food will change. I still enjoy eating & the taste & texture of food but I see it as something my body needs to function & not as something to comfort & soothe me emotionally - because I’m bored, sad, happy, angry, etc. I’m not continuously thinking about what & when I’ll eat next. It’s that maxim of eating to live not living to eat.
All the best.