I remember flying on the 777 just after their introduction on the BAH - LHR - BAH route and waking up in the middle of the night (BAH - LHR) feeling a bit short of breath and with an increased cardiac rate. An overall feeling of not being comfortable.
It only ever seemed to happen when the a/c was above FL380. Doesn't seem to happen now, maybe there has been a fix or I am just a bit fitter (lost a bit of weight and took up more exercise).
