If you made a commit, then it's not gone for good but recovering it is very hard. If you didn't commit your changes, then they are wiped completely.
If you remember your most recent commit number you can do "git checkout -B newbranch <commit hash>" to automatically checkout that commit hash at that point in history and give it a new branch.
Additionally, you can look at your reflog in TortoiseGit (it's under Browse Repository and Browse References) and you can see a log of your actual actions (it's like the Activity Log in Facebook). Using this, you can recover deleted branches and the like.