I would like to shut down my Stack Overflow account temporarily, because of personal reasons. I would like to still have it available, for whenever I decide to return. Is this possible?
I have seen a user asking for a voluntary suspension on their profile page, and they got one (perhaps after flagging one of their own posts for moderator attention, explaining this rather unusual request). For this to work, you'd need a way to communicate to the ♦ moderators when you want to return (unless you know upfront exactly how long you want to disappear). Fortunately, moderators can only suspend by sending a moderator message, which you can reply to.
If it's just to 'detox' from Stack Exchange, consider changing your password, while not writing it down and not letting it be remembered by your browser. That way, you'll be able to regain access to your account via the regular password reset procedure. Hopefully, that is enough of a barricade to login.