If you feel there was a blackout then you need to consult a doctor. Dehydration, certain medications, heart problems, untreated diabetes, and nervous system disorders can all cause this. TIAs or transient ischemic attacks can also be the cause. Certain epilepsies/seizures too behave this way with temporary blackouts. Do discuss this with your doctor and get yourself examined. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.