When impersonating as another user, cannot access the admin

The problem 

When impersonating as a user without admin rights, you are immediately locked out of cq5 admin, and cannot log back in, even as an administrator.

The Solution
You need to have read rights to the admin section to be able to log in, even when as an administrator. The cleanest way to get your admin user account back is to log out, by pasting the following URL into your browser. (Assuming you are on localhost and your port is 4502).

http://localhost:4502/libs/cq/core/content/login.logout.html