What has happened AFAIK is that the reinforced meshing inside the tyre rubber has been broken. This results in the bubble where the mesh has been broken as the rubber alone is not withstanding the air pressure.
I dont think this tyre is usable for a long period of time.
Well this is what i was told last year at a kwik fit when it happened to me.
yi, change it now. I ran flat on Thurs night and didn't even consider getting it repaired after driving for a few 100yds on it flat until I realised. Its not worth your life, especially when the roads are extremely slippy at the moment
Got my alignment done on Saturday. The guy noticed what looked like a bulge and a depression. He said that I must have driven it flat - which I didn't.
Tyre garage said the same thing but explained it could have been caused by hitting a kerb.
Either way, both urgently recommended replacement which cost me €180 - I had to buy two for the right match.
Frash, AFAIK it IS important to the cars stability under braking that the tires are 'paired'. So maybe you should go back and get a match for the replacement.
Tyres makes should be paired for safety generally but at the very least the driven wheels should match, if the car is front wheel drive you'll probably be fine.