It sure can be, especially when your lungs feel like they're going to burst and the surface appears to be minutes away. I had to dive to 53 feet for my free diving certification and it's very dark down there (seemingly more so than when you have tanks on your back:).
For anyone free diving at that depth, I'd encourage you to ensure there's always someone nearby that is capable of rescuing you.
Shallow/deep water blackout[1] is certainly dangerous with a buddy, but it's deadly if you're alone.
My fear going down farther than about ten feet is how long it takes to reach the surface. 30 feet is a long way underwater.
Rescue is related. I doubt anyone could pull somebody out that's passed out at that depth. You're just not going to have enough air. I had to help someone out of a pool once and the only way I was able to manage was by walking along the bottom with them on my shoulders to shallower area. They panicked and tried to climb me, pulling me under if I did anything else
Getting certified (at least for the association I use) requires that you are able to demonstrate rescuing an unconscious diver at the appropriate depth (after identifying their blackout).
Well done helping that person. Rescuing a free diving blackout has the benefit (for the rescuer) of an unconscious victim.
For anyone free diving at that depth, I'd encourage you to ensure there's always someone nearby that is capable of rescuing you.
Shallow/deep water blackout[1] is certainly dangerous with a buddy, but it's deadly if you're alone.
[1] http://divewise.org/science/physiological-causes-of-freedive...