First off, congrats on your sobriety. No one can take those four days away from you.

I won't sugar-coat it: simply stop dwelling on how awful it will be and go. You can go for as long and as seldom as you like and the only requirement is to simply say your name. If you don't feel better having gone, you never have to go back. But nothing in this world that's worth anything is achieved without a little suffering-and sometimes a lot of suffering. And the little anxiety you have now is a cheapest entry fee you will ever pay for the incalculable benefit of being able to snatch your life back from the jaws of addiction.
I'm sure that having gone, you will find it actually more pleasant than a visit to the dentist. And sometimes there are refreshments, which make it decidedly more pleasant.