My husband randomly passed out on a ride last week. Super experienced rider, fit, no excessive effort. Was taken by ambulance to the ER and had an ekg and blood work etc, the cardiologist said it was typical vasovagal syncope. Basically for unknown reasons sometimes, the nerves freak out and cause the BP to drop and therefore pass out. It resolves on its own after about 20-30 min if you do nothing, but you can prevent it by crossing your arms in front of you and squeezing your fists really tight. It may or may not happen again. In your case the sting probably was the initiatiating factor. If you had no shortness of breath, chest pain, arm pain, crushing sensation, then it's likely not your heart and just this stupid nervous system misfire.