If this is a long term behavior, I'd say from our experience that this is not normal. Perhaps there may be simple causes, e.g. too bright lighting. Also, our gulpers have periods of feeding a lot less than during other times, during which one may think their gulper has trouble finding feed until after lights out. It is usually is quite easy to hand feed your gulper and then one knows instantly whether they are hungry or not.
We haven't noticed our gulpers to get spooked. They appear to be pretty indifferent, oblivious to what's happening around them.
If yours spooks, one thought might be that the fish is stressed, uncomfortable and the reason should be sought and corrected. Gulpers are a specialty fish, harder than usual to keep successfully because they come from particular waters and need appropriate pH and hardness.
As noted in the last video, our gulpers all have a bit cloudy eyes and a small white speck in the middle, which may be the norm or maybe their reaction to our water, I don't know yet.