He seem to have syncope (fainting) attack.
It could be due to low blood pressure when he stands, or some cardiac or neurogenic cause. Consult a local doctor in person for physical examination.
Till then follow these things.
-Avoiding things that may provoke fainting
-Avoiding caffeine
-Increasing salt intake
-Staying well hydrated. Fluid intake should be increased to the point that the urine is clear.
Health Tips
avoid, sudden standing from sleeping or sitting position.