I agree with the above, from unfortunate personal experience.

Monday morning at work was not fun after 2.5 minutes sleep and I am exaggerating upwards!!

Unfortunately, my next HKG business trip is sandwiched between two already booked band three long weekends, so will go on the later flight to HKG to connect three hours after landing back at LHR and the earlier flight back for the start of the next weekend away. 747s both ways. ^

I expect to be an exhausted mess at the end of the 10 days.