I always lose weight after I stop working out... it's usually a temporary combo of two things: 1) muscle weighs more than fat and you've started to lose muscle mass, and 2) you increased your metabolism while working out and that hasn't stopped yet. It will.
I've been through this cycle quite a few times. My husband jokes that I'm the only woman he knows who hates being told I look thin. The important thing to remember is that when an illness mentions "unexplained weight loss," they're not talking about 5 or 10 pounds. Unexplained weight loss is losing 10% or more of your body weight in 6 months or less without changing your diet or exercising.
So, if in another month or two of not exercising or dieting you find yourself inexplicably at 177, you should see a doc (but keep in mind that this happens for all sorts of benign reasons). But I don't think that will happen. More likely, you'll do what we all do on this forum... you'll eat a bunch of food to see if you can gain weight and find yourself back at your "normal" upper weight, whereupon you'll sigh and realize you messed everything up and need to exercise again.