Sleep terrors can be due to anxiety or extreme stress. Since your sin is in this condition for 4 years now, get help at once. Early intervention is always better.
Feel free to contact for further assistance
Get help at once
Avoid taking non vegetarian foods at nights
Increase the intake of water
Go for regular walking
Based on the information you have provided, you have mentioned that your son has sleep terrors and is 24 years old and this sleep terrors has started since past 4 years. Sleep terrors are characterized by the person waking up suddenly from sleep appearing confused, could be sweating , appearing scared but unable to recollect content of dreams . Nightmares is a closely associated condition with the person waking up appearing scared and is able to recollect that there was a bad dream and the person suddenly woke up. Anxiety and stress can also be related to the psychological aspects of the night terrors where the concerned psychiatrist can clinically assess and advice psychotherapy accordingly for it. Sometimes neurological events and nocturnal seizures can have a similar presentation which needs a detailed evaluation by the neurologist as well.
Kindly consult a psychiatrist locally who can help your son with a detailed clinical evaluation from psychiatric point of view. Kindly consult a neurologist as well to assess from neurological point of view. Certain tests and assessments many be advised as well based on clinical evaluation and expertize. A sleep study assessment may also be helpful which the concerned psychiatrist or concerned neurologist can guide you about it. Certain medications can be prescribed by the psychiatrist which can be helpful to reduce the frequency of night terrors and can also counsel your son regarding the psychological overlay of stress, anxiety etc which maybe present additionally.
Do you know the reason for that?!
What sort of problems has affected him or lead him to this issues?!
If you know try to resolve those issues and he can sleep better.
If you feel you can handle that do consult a Psychologist in ur city and help to share all his feelings and learn to handle those issues.