Just thought I'd update you on this in the hope it might be helpful to other people with the same issue. You were right, it is due to something 'sleeping' and being awoken by the mouse wiggle. It is not actually sleeping as such but it appears to be switching from the Nvidia gpu to the onboard graphics after a certain level of inaction on the VR front. There is a setting in the Nvidia settings "Power Management Mode" which you can set for all apps or individual apps, this can be set to to Prefer maximum performance which should prevent it flipping to integrated graphics to save battery, however it is not the whole story, because I have everything set to use the GPU preferentially and Prefer maximum performance and it still happens though not as much. Something else is at work. Its more lag now than low fps. It will lag, the white hour glass suddenly appearing and nothing happening halfway through a load or during a timeline animation, and wiggling the mouse again seems to help. I think most people will not experience this you would need to have a limited system, be using a laptop (PCs don't typically need battery saving methods) and if you are using an Oculus you may find the fps reduction again. During a long load (sometimes 5-10 minutes for VAM or even some scenes) you typically remove the headset and go do something else for a few minutes, the Oculus detects its not on a face and sleeps, charging the battery through the usb and then when you put the headset back on and it wakes back up, you will usually see the low fps that can be corrected by the mouse wiggle. It is not a problem with VAM, it's more a windows/nvidia possibly/oculus thing.
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