You are right to be paranoid. If you're not using an secure connection (SSL), your email password is likely being transmitted via clear text and could be snooped by anyone else on the network (in fact, people set up open networks just to do this).
If you're connecting via SSL, or even better, have a VPN running, you should be fine. You can also log into SSL secured web mail (https), like
https://www.gmail.com/
Better safe than sorry.