Thanks for the reply.
The context was two persons discussing about a little health desease.
I wonder if the expression could reveal a sort of annoyance in the speaker's intentions.
In BrE, the tone of voice would be important. If someone simply said "Get yourself sorted" it may just be a useful suggestion. In the context you gave, I would
guess that the conversation went something like this:
Person A: How are you?
Person B: I'm OK. Well, actually, I'm a little worried about this mole/lump/rash.
Person A: Where is it?
Person B: Here. On my back. Look.
Person A: That looks quite bad.
Person B: I know. It hurts but I can't be bothered to go to the doctor.
Person A: I think that's a bad decision. I think you should get yourself sorted.
Person A basically means that they think Person B should go and get checked by a doctor and, hopefully, treated and cured (that is what "sorted" would mean).
In BrE, if "Sort yourself out" is said in a somewhat aggressive tone of voice, it can mean "Change your behaviour and stop annoying me" or something similar.