s doing. There are two possibilities.
Fainting after standing for a long time or
during rest, is usually caused by vagal hyperactivity that causes a drop in the blood pressure, usually with a slow heart rate. This is more or less normal. Diagnosis is usually confirmed with a head up tilt table test, where he's "flipped" from supine to standing position when EKG and blood pressure is measured.
Fainting with activity or high heart rate is almost never benign.