On my final instrument checkride in flight school, in an H13, I got something like that. In holding over an NDB, with the sun above and behind me, I got lots of flicker on the instrument panel on the inbound leg. I became so disoriented that I was having trouble controlling the helicopter. Cleared for the approach, I stayed at holding altitude until the beacon, then went down to PT altitude for the approach. At the MAP, I started climbing, then realized what I had done. The examiner let me fly the approach again, because I obviously hadn't busted any altitudes.
BTW, the reason the greenhouse window cover in the B412 is required is because of the flicker vertigo problem with the 4 blades - or at least so I was told.