Why does it occur and how to avoid the dizziness caused by the simulator and the goggles?

The non-medical term is called simulator sickness (it was first identified during the use of commercial airline flight simulators). It is caused when there is a disconnect between what your eyes see and what your body feels.  When I was flying a cinewhoop I had to sit down while flying to minimize the effects of FPV.  

Hi, Peter. Thank you for reaching out. If you use DJI Goggles 2 for the first time, we suggest you use a relatively low clarity, as the higher one may make you feel dizzy. We suggest you adjust the diopter when you can see the image clearly, or use the eyeglass frames and lenses with a proper diopter level. Thank you for your understanding.

I think low framerate will make it worse.  Mine is always crashing.

it occurs because your brain has not yet figured out how to segregate sensory inputs, visual cues and vestibular input. To avoid dizziness, best is to fly more and intentionally give your brain harder tasks - for example: fly sitting down, standing up, lying down, hanging upside-down (trippy af). Eventually you'll be able to "disconnect" and there won't be any dizziness anymore

fansebae Posted at 1-1 16:39
it occurs because your brain has not yet figured out how to segregate sensory inputs, visual cues and vestibular input. To avoid dizziness, best is to fly more and intentionally give your brain harder tasks - for example: fly sitting down, standing up, lying down, hanging upside-down  (trippy af). Eventually you'll be able to "disconnect" and there won't be any dizziness anymore

Thank you, I will follow your advice!

One thing that I find interesting is that I don't get motion sickness while flying the AVATA in real life. Can easily do 4 packs in a row, but I get motion sickness within 15 mins or so flying the simulator.

Just like with VR, its motion sickness. One thing you should never do, is push trough the sickness. When you feel it, stop immediatly and wait for it to go away. Then go "back in" till it happens again. If you push trough motion sickness, your brain will register it as something bad, and even putting goggles on or a smell linked to it, could make you already feel sick, as your brain tells you; this isnt good for us! Something that seems to help a lot of people who get sick in VR, is drink/eat ginger (tea) before they go into VR. Like anothe user says, the framerate of the simulator might be low (60fps or lower), this is also not ideal. You want atleast 90fps for a more lifelike experience, but phones dont do that. Frame drops will also make you sick.

If you have a nice pc, get LiftOff and train on that, so much better!