I did, somehow (think I pressed a hotkey), end up with this circle around the mouse cursor, which could select multiple vertices. I do not know how to leave this mode/tool, and I'm not able to do anything but to use this certain tool. I can't use shortcuts, for example cmd+S to save. I cant open any menu, I cant rotate the view, I cant do anything but to change the size of the circle (using the scroll wheel on the mouse) and to select vertices using it. No view hotkeys works (1-9)
Would love to at least get to know the name of the tool I'm stuck with, so that I could ask a more accurate question. Since I can't save the file, I don't want to close it. Therefore, if I could get some help soon, that would be very appreciated.