From what I understand, Diva, (and this helped me enormously during labour and birth), it *may* not be a problem, because it is (normally!) impossible for endorphins to fire at the same time as adrenaline, it's an either/or. My neuroscience books never mentioned exceptions to the rule, so take heart in that!
That's why breathing is so important - and not shallow TV breathing, either. Nice, big, deep breaths that make you feel nice...cos once you're feeling nice you KNOW that it is the endorphins responsible and you know that the adrenaline is hiding until it is required to come to play right at the very end of the process (essentially, expulsion of that baby).
Anyway, the HB post by Yogababy will elucidate this further, I'm sure.
Rule of thumb - if you feel good/relaxed/'zen', there is no adrenaline, because they don't fire at the same time