Since it's been almost ten days, I can write more details.

My brother, 19, never had any kind of psychological problems in his life. Two weeks ago, he was preparing for exams. And he became dull, as if focused on something all the time. He does get dull during exams because of overstudying, so it wasn't abnormal.

About one week ago, he had a little stomach problem, which wasn't a major problem. Then, he suddenly began over thinking about everything, especially his stomach problem(why it happened?, what was the reason? etc.). But not in a normal way, he thought about it for hours.

This thinking probably made him worse and he couldn't sleep for 2 days, until he took the pills. Later, his condition got a little better day by day. Now, he is himself at least, no extreme things...



But still, he has problems with his mind:

He cannot be sure whether what he sees is real or just a dream(or coma, hypnosis, etc.). He tries to do something to test it. This feelings/thoughts never leave him, though not always dominant.

When he sees something unusual(for example, seeing his school is empty which would be normally crowded), he seriously doubts it's real world. But doesn't do anything extreme, just tells us that he thought "Am I in a dream?".

When something goes wrong(like, learning we got wrong schedule for an event), his mood totally changes. His happy face disappears, and he becomes confused and thinks about it for hours.

He doesn't enjoy most of the things he used to enjoy. Sometimes he watches movies he used to like, but most of the time he doesn't want to watch them or play the computer games he used to play a lot.

He was an indoors person, now he wants to go out every now and then.

He didn't like his school at all, now he wants to go to school everyday.



If there's someone who has experienced such a problem(or know someone who did), leave a reply, please...

Generalized anxiety disorder could be a partial answer for your brother's condition.
It is characterized by excessive anxiety and worry usually over future events (the person predicts that something bad is about to happen and cannot control it).
People suffering from GAD have some of the following physical problems: restlessness or feeling keyed up or on edge, easily fatigued, difficulty concentrating or mind going blank, irritability, muscle tension, and sleep disturbance.

Best wishes!

Thanks for your answer.

He thinks about the present rather than future. Instead of worrying about future events, he is focused on what's going on now and sees unimportant, little details as important things. e.g. set the alarm clock, but later he checked and for an unknown reason the alarm wasn't set. It was enough to depress him for hours. Because it fed his "it's an illusion world, a dream; it's not real!" theory.

After the first 3 days or so, he seems normal and talks to us about his thoughts. That's how I know all of this.