What to do with my job?

[cinemasoul]

Hello, I'm new here, My name is Kat and I'm 25

Maybe someone here can give me some advice.

I have been "dealing" with anxiety and depression for about 10 years...
I have found a great job 4 years ago that I like and allows me to work about 3-4 times a week (there are two very busy months in the year which I have to work longer hours but I manage to struggle through it knowing it doesn't last long)

Recently my boss let me know one of the managers has been promoted and will be leaving, So she offered me her job as a manager.
I probably should have thought about it more but I accepted the offer.

It's only been a few days and I start to realize It's extremely difficult for me to work full time (5 days a week, sometimes can be 6)
It's more hours and more pressure and I can't handle it! I have been having really bad panic attacks at night crying and not being able to sleep.

I have scheduled a meeting with my boss to let her know it's very difficult for me to work full time.

What can I tell her without letting her know about my anxieties?
What if she offers me to go to my old job back? how will it look in the company that I got a promotion and got back to my old job?

I even thought about quitting the job and looking for an easier part time job.

What if she offer me to stay in this position but to work less days (unlikely) I don't know if I can handle the pressure of being a manager!

I appreciate any advice. Thanks.