I can't believe all the people insisting that travel sickness is a one size fits all condition and that OP can't possibly have it and not have vomited for 5 years.
I had awful travel sickness throughout my childhood on buses and in cars, but was okay on trains and planes. In childhood we didn't have a car and would use buses frequently. I would often go white as a sheet and feel very sick during the journey and for several hours afterwards.
I wasnt given travel sickness pills because the "only ones that worked made you stroppy".
I still have awful travel sickness but manage it better by avoiding buses and being a passenger in a car unless its absolutely unavoidable. Plus carefully controlling the environment in the car as. a driver so its not too hot or stuffy. Most people I know dont get travel sickness as a driver, but not me. Especially as a new driver I could often be seen seen with windows wide so I didn't feel horrendously sick even in the rain and cold.
Despite suffering periods of intense travel sickness where I felt like I desperately wanted to vomit every single time I've been on a bus and 90%+ as a car passenger I was very good at stopping myself actually throwing up.
In fact in my entire life I can only remember 4 occasions when I actually vommitted. The first I was very, very young and on a regular bus journey. We had to get off and I vommitted all over my new outfit. The second I was around 6 years old and on a long journey to the seaside. Squashed in the back of a hot car. I had to get out and vommitted several times into a bin at a service station. The next over 25 years later I was stuck in a stationary traffic jam driving my car with the window open and no air flow in a stuffy car. The last five years later friends were driving me to my wedding dress fitting and showing off their cornering on country roads. I thought I could cope with the window open, but couldn't and made it out of the car in time but threw up over my beautiful ivory wedding shoes.
So four occasions in over 30 years when I actually vommitted, but I would still class myself as having very bad travel sickness and have literally spent thousands of miserable hours feeling like shit.
So I can totally relate to the OP not having vomited in 5 years and not having considered it might happen on this particular flight. She has my sympathies, particularly with young children to look after at the same time.
Interestingly all of the times I was actually sick I had reduced air flow (hot day, extra stuffy vehicle) and so can easily believe that the mask may not have helped when already feeling sick.