What happens on board will depend a little bit but if you make it clear that you want to sleep and NOT be disturbed for meals until you wake - then no probs.
Fasten your seat belt over your blanket and away you go. The carrier web pages should give good details of the time of each sector. For example, LAX or SFO are usually +/- 12 hours wheels-to-wheels from LHR so time to sleep, wake naturally, eat and be ready. Also, whether you can eat on demand, or simply snack on demand.