This one came out of nowhere. I was fine at JFK, having a drink with a colleague, then I got on the plane and sat in my seat and suddenly my throat started to tickle and by time I deplaned it was full on. Taking a couple of ibuprofen pills felt like swallowing two bowling bowls that had been wrapped in barbed wire.
Same thing happened flying back from San Diego last year. Got on plane feeling as fine as a man who's just quaffed a couple of Stone IPAs can be, and then spent the entire long flight feeling worse and worse. And for bonus points, some massive snafu on the M25 at rush hour meant it took an additional two-and-half hours to get home. And despite my looking and sounding like an extra from The Walking Dead the taxi driver talked at me for the entire journey.