You can do what you like: Listen to your favorite music, sleep well, chat and talk out with friends, eat delicious food, or just cry and relax.
If the depressed mood was preceded by severe emotional upheavals - the death of a friend, relative, parting with a loved one, loss of a job, an acute episode of violence - then the person may also need the help of a psychotherapist.
Also, changes in mood and behavior for no apparent reason can be observed in people with various brain defects associated with:
the consequences of infectious processes (meningitis, encephalitis);
benign and malignant tumors (many patients recall that the first signs of the disease were changes in behavior and mood).
First you need to come to a therapist, since such conditions can be observed against the background of hormonal disruptions and other somatic abnormalities. He will give the necessary directions. If the examination does not show the presence of a physical illness, it is necessary to have a consultation of psychotherapist.