I was absolutely fine (save for the swelling etc) for the first four or five times I got stung, and then one day I rocked up to a hive to put an entrance reducer in because of wasps and foolishly didn't suit up thinking I'd only be there at most four seconds. Took longer than expected as the reducer had swelled in the rain so it was tricky to get in. After several minutes faffing, two bees came out and stung me between mouth and nose. Quite right too. The hubris!
Felt fine at first, got back home, started feeling panicky and nervous, then whole body came out in an instant rash that was so itchy you would have thought I was Lady Macbeth trying to get blood stains off. Then got breathless and that was the point we called 111, and they got the ambulance round asap and had a trip off to A&E.
Long story short, now have a pair of Epipens and a proper pukka bee-suit and I wear wellies and gloves for ALL inspections and even routine little piddly jobs near the hives. Also booked on an anti-bee-venom-allergy treatment.
Of course, since then, I've been stung (through the veil when collecting a swarm) and had no reaction at all, so I don't know if the venom was particularly potent that day and it was the double-sting dose wot done it...
I did see something the other day about an angry bee can increase the potency of its venom, as opposed to a reactive-sting, so perhaps it was me winding them up with the reducer got them to brew up a mankiller dose. No idea - better brains than me on here might know if this is true.
Edit:
Angry bees produce more protein-dense venom - phys.org