It’s a sign that something is probably wrong. Sometimes if you get very angry you can also self harm because taking it out on object or other people is illegal, and it can relieve some of that rage to smash your hand through glass or stab yourself etc.

If you feel any emotion super intensely (I have BPD so I feel them intensely a lot haha), pain can seem necessary to distract you just so you can calm down and focus on the pain. This is the same reason I think depressed people do it (that or its a cry for help/attention but that would still suggest there was something going on if they were that desperate for help/attention that they’d start mutilating themselves)

Anxiety it’s not usually connected to, but I suppose if you pick at things or bite things nervously then you could cause harm to yourself in that way (bitten down nails) skin picked off, cuts etc.

I think there are other signs of mental illness, I know self harm can be a criteria for certain illnesses but it’s one of multiple (so you have to have for example 6 out of 8 or something to qualify etc).

Definitely would suggest that something isn’t fine. It might not mean they have a mental illness, something bad could have happened to inspire it rather than there being something wrong with their brain, but it’s a sign there’s something wrong.

Maybeee if a person had something horrible happen (like their loved one died or cheated or etc) and they punched glass or something and that injured them that could be considered normal because it is a human reaction to seek a distraction but I’d say self harm doesn’t necessarily indicate a disorder, but it does indicate something is wrong