Interesting question. It is definitely possible for hair to fall out after any kind of stress including surgery. The cause of this type of alopecia is unknown. In fact the causes for most alopecia is unknown but stress probably has a significant role. I have had only one case in over twenty five years of stress induced alopecia (after breast augmentation) so it's pretty rare. It this particular patient it got very thin and did not fall out in clumps or leave her with bald patches. The hair will regrow but can take a good 3-6 months to get back to normal. If you are particularly worried you could pre-treat yourself with Rogaine which should help to stabilize your hair.
Thank you for your question. You do not have to worry about your hair falling out after your surgery. Best of Luck!