I had exactly this rash/hives which got worse and worse over 24 hours, until I eventually collapsed with extremely/dangerously low blood pressure. Turned out it was from newly prescribed Naproxen, which were supposed to be "better" than ibuprofen or diclofenac which I had previously taken for arthritis. Was told that the allergic reaction was so bad it was no longer safe for me to take any NSAID (non steroidal anti inflammatory drugs). Rather a nuisance but would never risk it again!
Mark Carney is becoming the new leader of the western world


