I can't think clearly anymore

I feel like I can't think clearly or function normally, and I feel very slow all the time. Things that would normally be effortless and easy for me feel more labored and take me longer than they should, and it has hurt my performance at work a lot. I feel like I can't even form a coherent thought.

I have been dealing with a lot of stress and I haven't been able to eat because I constantly feel sick to my stomach from anxiety, and i've started smoking again to cope with the stress. I've also just found it more difficult to maintain my personal hygiene, and I feel exhausted no matter how much I sleep, and it has become difficult to hold a conversation with people because i'll keep forgetting what im talking about and have to try to recall what we were talking about.