I do it all the time, Haibane, it's very easy to change the layout accidently. On the right side of the page, just above the active PM, you should see two small left-pointing arrows. Clicking those will change the layout so that you have the left-hand menu visible again.
Clicking the double arrows in the Messages menu header will hide that menu and give you a full screen message window.
Not sure about the profile window though, but it could be the same sort of thing. Just look for two little arrows to hide and show the side menus.