Does anyone know what is actually causing this? I mean, it's not a virus right? The solution is presumably sterile, so it must be some kind of reaction then. It's a mystery to me. I was so glad to hear that I wasn't the only one feeling like shit the next day after each one, but I'm still curious about it, 'cause it's just like a flu or cold or something. I've had good luck taking Benadryl. But the relief that gives could be psychosomatic, and I'd prefer to not have to take something that makes me tired. Thanks for posting the question.