I've seen dream sequences in italics like in Dark Rivers of the Heart by Dean Koontz. Check out that book because it's a good example of how to make dreams gripping rather than draggy and boring. It's told as a story sometimes but also picks up in dreams, revealing a mystery from the past, always continuing where it left off.
Some writers switch to present tense since in our minds a dream unfolds in real time. We're either immersed or observing. I have one small dream fragment that shows a difference in a reoccurring nightmare a character experiences and then later I have the dream how it should be. The dream unlocks a small mystery I bring up in chapter 1. I switched to present/first because it needed that intimacy and immediacy.
I've read many agent blogs and beginning a novel with dream sequences is frowned upon since it's done so often. From an unpublished writer, it comes across as gimmicky. If you need to begin with a dream, keep it short and vivid. But honestly it's a risk. You must make it worth it.
For visions, you could also change up the rhythm and tone instead, like using fragmented pieces, as imagery rushes into your character's mind, rather than writing out complete sentences. This technique would always indicates a vision is unfolding, without needing a change in font.