I frequently had that everything on screen would just disappear or that I'd randomly died. Another issue is that I had no idea what I was looking at. So the first time I was randomly strolling around and after 40 seconds started to try out stuff like what are those glowing lines along the walls. Can I touch them? At some point I saw question mark boxes so I tried to pick up those, but nothing happened. Or I encountered a sign of other live moving around. Should I touch those? I died, so apparently not.
For you the developer it is clear what everything is, but not so for the player. You have to somehow communicate this to the player. Either by using concepts that they are already familiar with, like spikes and pits or scary looking enemies. By outright telling them, or by making sure they experience what they are early in game.