Seizure, heart attack, stroke are all pretty common in that context. They generally would have other symptoms such as pants wetting, chest pain, or not being able to move something. A sudden and temporary change in the heart s rhythm would cause black out and hyperventilation and might not have other symptoms (death, yes, death is also quite a common symptom also associated with heart rhythm change). Pretty much by definition any use of drugs that makes you pass out is an overdose. My kid faints at needles and blood so, zero drug amount injected in him would technically still be an overdose. It s a really bad sign. It is likely to mean something broke like a mild heart attack or change in the hearts electrical properties. and this would be a reason for a pretty thorough evaluation.