Stress, anxiety, and dramatic events can all cause these experiences in my opinion. "Mental exhaustion" can lead to fatigue which defintely can make us feel like we are not ourselves. I think this is quite common with many of us here in this community.
I believet he best way to deal with it is to confront the source of your anxiety. Do you have access to counseling? For me, talking it over with a professional, shed light on why I was feeling the way I was feeling and gave me the tools to confront it. Keep us posted.
I have looked at nhs counselling but there is an 18 month wait here at the moment.