Reasons for hairloss

I am curious about the reason behind hair loss. In the past I have had a hysterectomy, a surgery to clear up a severe infection from that surgery, my gallbladder removed directly after that, and knee surgery in 2012. I can't remember any hair loss after those surgeries, unless I just didn't notice it.

Is the hair loss from having surgery itself? Or is it from the type of surgery?

It is a side effect of having anesthesia. Google telogen effluvium

Caused by the initial drastic reduction in nutritional and vitamin intake. If it was the anesthesia you would have seen it in prior surgeries. 

Holly is correct - it is due to the surgery/anesthesia, not the nutritional deficiencies. It does not always effect everyone, but it's very common and no way to prevent it. As she stated google Telogen Effluviums.

I think you didn't notice it .. When I had my C-Section and  Sigmoid Colectomy, I lost hair both times.

There are lots of reasons for hair loss after weight loss surgery. The list includes a reaction to anesthesia, but can also include other factors associated with this specific surgery such as anemia, vitamin b deficiencies, lack of protein, dramatic weight loss, physical and emotional stress, and hormone level changes. There are a number of other factors that can affect your hair as well that are not related to surgery, like heredity, excess vitamin a, medications, autoimmune diseases, etc. 

I had three normal pregnancies, took my vitamins, got lots of protein, didn't have anesthesia and lost hair each time. Had WLS and two rounds of plastics under general anesthesia and didn't lose any hair. 

I was going to ask if folks had subsequent loss from PS. Nutrition/hormones appear to be the smoking gun to me.

My surgeon said its due to rapid weight loss

Telogen Effluvium is caused by some kind of physical trauma to the body - such as surgery, childbirth, or chemo for example.  It has nothing to do with nutrition at this point.  Any extra protein and vitamins you take will benefit the new hair emerging that's pushing out the old - but it will not prevent the old from shedding.  It starts around 3-4 mos after surgery, lasts a few months and stops.

If this occurs again later on without any physical trauma to the body, then you should be looking for nutritional reasons.