I see @invoice05_volcano's point and partially agree with them. At first glance, there does not appear to be an argument here.

The statement "With my current medical condition, there may not be another alternative" (hereafter P) does not appear to support the statement "I've decided to go ahead with the operation" (C).

Upon further analysis however, one could argue that P does weakly support C.

We can pose the question, "How do we know the author has decided to get the operation?" If our answer is "...there may not be another alternative" then P does appear to be a premise.

But as @invoice05_volcano points out, this is up for interpretation, as P appears to rather be supporting an implied premise; specifically, "I need to get the operation" or "I should get the operation".

A statement which would better serve as premise to C would be "I informed my doctor I'd like to get it done, and I've booked my operation for next week". How do we know the author decided to get the operation? Well, because they confirmed their decision with their doctor and booked the appointment. Clearly a premise to C, and thus clearly an argument.

I do not agree with the reasoning from @nikk.ia262 above when they say "... All we know is that the author argues that he has no choice but to go with the operation, because of their medical condition and there’s no other alternative. ..."

The author is not claiming that he has no choice but to go with the operation when he states "I will get the operation". Were C instead "I need to get the operation", this reasoning would be valid.

At the end of the day, language is always up for interpretation; this is not an exact science. I'd lean towards this not being an argument. Whether the LSAT writers would agree with me is another matter :)