I agree that it can go both ways. Cycling can help shake off a bad emotional state, but it can also cause poor performance. The first time I was fully aware of the latter was not with myself, but with my friend. We were doing a usual ride and she wasn't feeling so great so I was doing most the pulling. The further we went, the slower we went and it was clear she was REALLY not doing well, very uncharacteristic for her. We pulled over and she started to cry. I found out she was going through something pretty deep. We turned around and went to a coffee place and she unloaded on me.

I've experienced both as well. I think it depends on how deep the emotional turmoil is as to whether a ride can help or just be miserable. Sometimes it can help even though you can only go at a slow speed. Just getting out and lolly gagging can be therapeutic, but sometimes riding as hard as you possible can can help get your aggressions out if you are physically able.