Please enter your Profile by clicking on the sculpture of the head in the top menu bar. On the bottom right side you will find a field "Dialogs". Tick the box "show all", and you should be seeing all pop-up-messages again.
You can also click on the medicine bottle between your name tag and the Professor in the top menu bar, in order to see your last actions. These will be saved here until you leave the game or are logged out automatically after 2 hours.