ZSH removed, cannot relogin

The guest user is not granted the permission to run sudo or pkexec, which (unless you're root, which you're not) are required in order to change another user's shell.

So the only solution occurring to me is booting into a root shell and changing the user's shell as root:

chsh -s /bin/bash user

Where user is your user's username.

So additionally to what @kos said..

For some reason I added source ~/.profile to my .bashrc file (don't know why.. read it somewhere) And my .profile file loaded the .bashrc which cause circular loading!.

Removing the source.. + @kos solution did the trick!

Login as root or boot into root shell and edit the shell entry in /etc/passwd to "/bin/sh". Then you can login again as yourself and change things from there.