Your problems are most likely caused by sending an XOFF character to the server, by pressing CTRL-S. The XOFF character is a flow control character, which instructs the server to stop sending data. To undo this, you need to send an XON character, which you can do with CTRL-Q.

Misfortune would have it that CTRL-S is the forward search command of the readline library. This makes searching in your bash history, among other things, a little annoying. Luckily, you’ll mostly use CTRL-R, for backward search, but sometimes you need a forward search as well. I would welcome any suggestion as to how to use CTRL-S without having your terminal freezing on you. The terminal program I use, Putty, doesn’t seem to have an option for it.