Bus and Coach Sickness
While long distance coaches offer a reasonable experience for most people, local buses can be another story. Anyone prone to motion sickness has to contend with a combination of cramped seats, stuffy atmosphere, engine fumes, jerky vibrations and constant starting and stopping.
Personally, I have a problem with the swaying movement as the bus lurches around bends, and the engine fumes (which is worst towards the back of the bus).
You'll feel better sitting right at the front, as close to the driver as possible. Face forwards and try to look out through the front windshield. Follow the route with your eyes, anticipating any bends in the road, bus stops etc. Try to open a nearby window if possible. Listening to music with headphones may help, but trying to read will only make things worse.
Coaches typically stop less frequently, use main roads and have a higher passenger area with more comfortable seats. Nevertheless, if you are prone to sickness, it's not wise to try to read. Sit back in your seat, relax and try to focus your attention onto something not travel-related. Many coaches have a air vent over each seat. Turn this to direct the air onto your face.
Carry a bottle of water with you and take regular sips from it. You may also find it helpful to suck on peppermints of other candies. Avoid anything greasy such as potato chips.
With both buses and coaches, if you think you're going to be actively ill tell the driver
! The embarrassment of having the bus stop for you pales into insignificance compared with the misery of vomiting on board.