Many people on the trek had problems sleeping due to altitude, digestion issues or other rreasons. I recommend taking a blindfold (which I luckily kept from my flight) plus some good earplugs. Locals are often up in the early ours preparing yaks or making tea and these help shut out any disturbance and maximise your beauty sleep.
Applying a fungicidal powder to your feet each night helps keep them in good condition over the 18-day trek.
I was the only one of the group of 13 not to suffer stomach issues on the trek but I'd recommend taking along plenty liquid handwash, being religious about using it, particularly before eating, and also taking along a course of antibiotics (on the advice of your doctor) in case you fall foul of the local bugs. A few people also developed chest infections alongside an annoying dry hacking cough, as it can be very dusty, so I'd also recommend taking along antibiotics for this as well as a box of lozenges.
The above makes the trek sound like the 'walking dead' but it's not, as long as you look after yourself, I promise!