I induced a lowered metabolism through extended keto dieting (10ish months) + heavy weight training. It was extremely unpleasant. I suffered symptoms of hypothyroidism, including bradycardia, orthostatic hypotension, poor circulation (cold extremities), severe constipation, fatigue, dark circles under my eyes and other things. My personal belief is that an infection triggered the worst of the symptoms, but the signs were there before that.
"Starvation mode" is a tricky thing, and a phrase that I think is overused in dieting circles. But the knowledge that you depress metabolism on extreme and/or extended low calorie OR low carb diet is pretty well-established and non-controversial, and for me it kicked it really badly at around 13st 10lb or so. You don't have to be stick thin to suffer from it.
Please do take care of yourself.