This Tiny Owl That Fell Out Of Its Nest (Don’t Worry, It’s Mum Came And Got It Later)
Coming from personal experience, I often cared massively for other people and their well-being, hoping that they would do the same for me. In the midst of this I became 'the helper' yet I found myself never being helped. I suppose in a way you stop caring for yourself and start only caring for others.
People that are suffering and feeling isolated will start to lose their ability to thermoregulate. They will feel cold all the time. This will lead them to wear extra layers or heavier clothes than would be normal for conditions, taking longer hotter showers, always the first to grab a throw to cuddle under. There's a potential evolutionary reason for it, if you're feeling lonely and isolated, then your body telling you that you're cold will force you to get closer to those in your pack to stay warm. Close physical proximity encourages better bonding. Better bonding ends loneliness.
Now, some people are what we in The North call "freeze babies", that is to say that they just don't tolerate the cold. And some people are really like that. Some people just are colder than the rest of us. But if you're at, say, the beach and everyone's out in their swimsuits because it's just too damn hot otherwise, but you see someone off by themselves in a sweater and pants looking pensive, nervous... that person's going through some [stuff].
Lack of interest. Gamer all of a sudden no longer games? Gardener let his plants die? Social butterfly now hides in a cave?