Translation:Here come all the emotions all at once.
First, it is "alla" but perhaps that was just a typo. The best I can think is that "känslorna" by itself means "the feelings" or "the emotions". The sentence without "alla" would then translate as "here come the feelings all at once".
This implies a certain subset of feelings (e.g., maybe just anger and happiness), whereas the "alla" makes clear that the whole range of emotions are coming.