If you've set a particular DATABASE to single user mode, ie., , you should still be able to connect to the SERVER and have your connection set to another database, like for instance MASTER which is probably the default database associated with your login. The one exception I seem to notice that if in SSMS I set my DEFAULT database (as speced in SSMS properties for my "login") to the same database that I for whatever reason set to single user and THEN LOST MY CONNECTION, then yes I was pretty much locked out with SSMS. So you'd probably not want to set your database to SINGLE_USER if it is the DEFAULT DATABASE that your login is associated with.

So thats an interesting situation that I wasn't aware of.

Trying Lowells solution I was able to log back in with:

ALTER DATABASE TEST SET ONLINE

BUT ONLY if I added:

ALTER DATABASE TEST SET MULTI_USER

---> USING MY EXISTING CONNECTION THAT I HAD OPEN <---

If you've set your SERVER to single user mode, ie., startup parameter -m, that looks to me to be a different situation.

edit: grammar