Hello and welcome to Beyond Blue. This is a huge topic with all sorts of issues hanging off it. Let me say up front I have no personal experience of bariatric surgery, but a friend had this surgery and lost a huge amount of weight. It's a topic I was interested in and I asked her how she was managing, was it easy? She battled through the change of lifestyle with the help of her adoring husband and I imagine her adult children.
I think you would have been to one or more psychology sessions before the surgery. Can you return to this psychologist for further discussion or perhaps a referral to another psychologist well versed in bariatric surgery and it's outcomes.
I love the way these so called expects make pronouncements on how people feel and decide that the impact of of a particular type of surgery. After surgery and probably for the next six months at least but more likely 12 months, there is a huge impact on the way you eat, what you eat and how you eat. This is where you need so much support and for the same reason you put on weight. There needs to be someone to help you eat only the amount of food your body will allow at any one time and provide reassurance, comfort and support.
I am certain anyone who had this surgery will feel so much better simply by being thinner and of course all the illnesses that hang off obesity become less likely. One reason I can think of for someone becoming depressed after surgery is the flat feeling once the surgery has been done. It's almost an anti-climax. You feel different but the weight is still there and will be for a while, though slowly going. I think we build up life changing events and get very disappointed when nothing much changes immediately. So maybe that's a reason.
What I know of depression, and remember most of what I know is from my personal experience, is that it hits without warning and often those people who are considered less likely to be impacted. It may be you have less resilience to counter depression, and remember you have had major surgery and recovery takes time.
It is interesting reading your comment about the increased likelihood of suicide in bariatric patients. The expectations from this surgery are high but require the patient to be very aware of the food they eat. I believe you can never tell another what this will feel like. The other thought I have is about the realisation that this surgery is irreversible so no matter what the patient wishes they are stuck with it.