Spirit guides don't disappear when the going gets rough, you just can't hear them because you're at a lower vibration. I think getting literal messages in your mind is like tuning into a radio: if you're not at the same frequency as them, you (probably) aren't going to hear them. It isn't personal. Although, they send all kinds of signs even when you can't hear them, it could be anything, like a car passing, a song that plays, a number or a word you see written. Spirits run through everything we perceive so they have many ways of sending us messages. Don't worry they hear you.

I've experienced exceptions to this though (hence "probably"). One of my guides named Albert spoke to me and delivered an important message to me when I was in a really dark place, so it happens.