An average user of social media feels that he is underperfoming and his self-esteem is constantly decreasing.
I used tenses in this sentence instinctively, and after I had finished I started to wonder whether it is okay. And I am not sure about it.
I guess that one feels something anyway, hence simple, while underperforming and decreasing are continuous "actions" which can be easily stopped, for example by quitting social media.
So, I suppose it would be quite awkard(?):
An average user of social media feels that he underperforms and his self-esteem constantly decreases.