As narrated by you, there are two most likely possibility one is syncope and other seizure. But syncopal attack is more plausible diagnosis as your loss of consciousness was postural and is associated with lightheadedness at onset. Seizure episode usually begins suddenly with abnormal jerky movements of limbs, neck deviation, tongue bite, incontinence and unrolling of eyes. Fortunately you don t have any such complains. For investigation regarding syncope you need to get you blood pressure measured, ecg of heart. For treatment you should increase your salt and water intake, move legs before arising from bed or sitting position , leg stockings also helps. If all this measures don t help then medications may help. Avoid crowded and humid places and tight collar dresses. Consult a doctor for further evaluation. Hoping for your good health.