Doesn't have to be awful. The collective wisdom is to stop immediately if you start to feel ill. Trying to push through will not go well. Eventually, most people build up a resistance to motion sickness ("VR legs"). Bonus is that this motion tolerance carries over outside of VR. Several VR users have reported being able to read in the car for the first time!
That said, it requires several weeks of repeatedly exposing yourself to awful motion sickness that may take hours to disappear.