>>311655387
Cheap desktop fan is a great training tool because it will remind you to breathe whilst wearing your headset. 
Thats what I find to be a big cause of peoples nausia. That slight pressure of the headset being on their nose causes them to breathe less or stop breathing for periods at a time and that lack of oxygen combined with the extra head generated wearing the headset accelerates the nausea from the cognitive dissonance.
Point that sucker at your face and you'll realise how much you stop breathing and make an effort to breathe in more. Just a quiet deep breath every minute or so is all you need, that, and the exposure tolerance you build up will eventually let you stay in VR for hours. (Though take regular breaks too. To be honest at first I would keep sessions to half and hour, then 45 mins and then an hour for a while. Low motion stuff, fixed turning and view boundaries at first are helpful too)