To run a VRMark benchmark or experience on your VR headset, go to the OPTIONS screen and set ALLOW CONTENT TO RUN ON AN HMD to YES.
When you use your VR headset as the display, the frame rate will be capped to 90 frames per second. You will not get full result details. The benchmark tests use an animated camera. For your own comfort, you should not wear your headset while the test is running.
Some headsets, such as the Oculus Rift, detect whether the headset is being worn. You will need to cover the proximity sensor with your finger or tape, or you can place the headset on your forehead rather than over your eyes.