It's anxiety, trepidation, I believe. In the following, emotions equal what is sometimes called (emotional) valence, salience or meaningfulness. I see emotions as valency/salience, anxiety as something separate. Emotions positive, anxiety (also, in some ways) negative.

Claustrophobia, agoraphobia, fear of mania and fear of depression. First two (mostly) figuratively.

As long you can see where to go, things are more meaningful than other things, you feel fine. You can see contrasts, as it were. You have a feeling or direction. When things are always the same you feel confined. Anxiety fills an emotional void. You are lost and stuck. You panic.

If you see few possible ways to go, thing get increasingly more meaningful, you feel great. You have a very strong feeling of direction. When you then reach a dead end or you fear you might, you suddenly feel confined. Anxiety fills an emotional void. You feel cornered, overwhelmed. You panic.

The moment of panic is the switch.

The moment you are completely blinded by darkness and the moment you are completely blinded by light. Seeing nothing and seeing just a little are very, frighteningly different.

But the panic may set in sooner once you associate the change in light with either depression or mania. If you do, you might pole-switch to the other extreme again. You might keep on panicking, leading too rapid mood fluctuations. That might depress you in itself, (only) rationally. Thoughts begin to play catch-up with your emotions, mixing things up.

It's loony tunes.