Hi, I get the same problem. It starts with an irritating itch in my eye, usually the corner, or a runny nose, sometimes both. Then bang, within anything from five minutes to half sn hour my face swells up, especially my upper & lower eyelids till my eyes are just tiny slits in beach balls, just awful. I look & feel like Elephant Man. Sometimes, later, my face behind to burn too & I get rashes on my arms & chest.
It just seems to come out of the blue, no obvious cause. When it first started,a few years ago, my GP sent me to an allergy consultant who did blood tests. He changed a drug I was on, for an ongoing condition, thinking it might be that & said other than a mild allergic pointer for a grain not severe enough to cause the reaction, he was a bit stumped. He gave me a direct number to his office in case it flared up again but unfortunately he retired soon after. It's happened lots of times now, had other tests, nothing showing up as an obvious cause. But the last doctor I saw, a locum standing in for our GP who seemed more clued up about allergies than she is, said it's often impossible to pinpoint a cause of this facial oedema type reaction. It can be absolutely anything. Even something as hard to believe as someone walking past you with something on their clothes, industrial or something.
He said all you can really do is be always prepared to act fast to co bet the symptoms. Carry Piriton always, take at least two at once, four if you can feel it getting bad, then another an hour later & another after another hour. Then carry on with the dose on the box. Get antihistamine eye drops. Chemists & Tesco sell Opticron & use them at the first sign, four times a day.
If you have it bad though, do see your doctor. I have Piriton & steroid tablets along with steroid & Opticron eye drops on prescription to keep handy for flare ups plus a daily antihistamine & an Epipen in case my throat begins to close up. Please take it seriously & see your GP as you never know which episode is going to turn severe very quickly.