Oh you will know, in fact you will KNOW, with no shadow of a doubt, and really wish to god you didn't.
My g/f went through it once not long ago, after a sudden, unpredictable interaction between a triptan migrain medication and daily SSRI treatment, had taken both together many times, and all of a sudden, the shit hit the fan.
Left her collapsed on the floor in agony, unable to stand or do much of anything.
She would have called the hospital, but by the time she was able to move she had begun to recover. Thought she was going to die at the time, scared the piss out of her, not to mention me when I found out, and she doesn't scare easily at all, for the lady in question to think about seeing a doctor, it takes little short of a mauling by a rabies-infected mountain lion, or a swim in a lake full of starving pirhana.
Unless perhaps it happens, and you were 'lucky' enough for it to be the merest hint of a bad reaction from a tiny dose of whatever combination triggers it, you will damned well know about it.
If you needed help, there is every chance you would be sufficiently incapacitated to seek it.