No, it is not OK. If your glasses prescription is right for you it should not cause eye pain or nausea, it may cause a bit of discomfort but not to the point of pain and nausea.
Sometimes in cases like yours when there is a serious change in prescription we don't give the full correction right away, we correct to a certain level and ask to visit us again in 3-4 months to update the prescription. It is not in order to sell another pair of glasses it is in order to avoid these kind of issues with eye/head aches and sometimes the eyesight even stabilises in a lower prescription if we do so.
I'm an optometrist.