It's only expected that you would be having extreme anxiety over this...it is a hard thing to do to have to put a pet down, My advice to you is to allow yourself to feel what you are going to feel. You are going to go thru the grieving process, like cj stated...you will feel sadness, anxiety, anger, etc.
Maybe for a few days, take the Ativan every 6 hours as prescribed, and after a few doses, you may notice some relief. You can also consider calling your doc about perhaps trying a higher dose (ie 1 mg) as needed to see if it is more effective.
Just know that this period is going to be painful, there is no getting around that...and like I said...allow yourself to go thru all of the emotions associated with losing a family member, which of course....is what our pets are.
Lastly....remember that you're doing this for a wonderful reason.....to spare your dog suffering. Despite how much you love him, sometimes making these decisions requires us to try to put our feelings aside and consider what is truly BEST for our furry friends. Ask the vet for any keepsakes, or burial options, to help with closure. I know many will offer a remembrance momento, that would include a lock of fur, photo, etc. Also, try to remember the happier times, and how much joy your dog has brought to you. As hard as it is to lose your dog, it is part of the process of adopting and loving a pet. As horribly hard as it is....it's worth it, b/c you will carry those memories of him for a lifetime, and the pain WILL get easier with time.
So very sorry you are going through this, if we can be of any help, we are here. Hang in there.
I am sorry about your dog...I know they are part of the family. Do you have some counseling that maybe be available to you? Grieving is a natural part of life when we lose someone we love and in my experience, it can help tremendously just to sit down and put it out 'all on the table.' I am sorry for your loss...please keep us posted.
I'm so sorry that you have to put your dog to sleep. I'm a pet owner myself and know how painful it is to lose one.
If you've been doing well all this time on the Prozac and just need something to get you through this terrible time you might want to consider Valium. It's easier to quit than Xanax. Just take it as needed only.
Again, I'm really sorry about your dog. We're here to listen, okay. Take care. Remar