One should not speak of "hallucinations" (images that take the place of reality) but of "visions" (a broader and more complete vision of that reality). Both possible effects may or may not occur; and they neither happen always, nor to everyone, nor do they respond to the same motive.
Visions are one of the many ways in which information can be received during the session, and it depends a lot on each person.
More important than the vision, is the comprehension that can come, with or without vision, which gives us the guideline regarding what we will be able to take into our daily life.
Vomiting can respond to physical or emotional cleansing (purging), or also to the release of thoughts, emotions, feelings, patterns, beliefs, etc... that we have been carrying with us for a long time, and which it is no longer our turn to hold