First of all, if those visions are haunting you, then I would recommend that you stop reading/watching/looking at such info about animal cruelty. Since you're vegan, you know what happens and don't really need to see it again. There's no point in tormenting yourself.
When I can't clear my head, I find that reading helps. It makes you think about something else, and then when you're too tired to keep reading you can just nod off.
You could also try listening to music/radio as you drift off.
And meditation may help you.
Occasionally the sadness in the world weighs heavy on me, but most of the time I find I can deal with it. The thought that helps me cope with so much suffering is the knowledge that I do what I can to help end it.
Perhaps when you have those visions, you could make a silent promise to those animals you are reflecting on that you will do your best to make sure it doesn't happen to any more animals. And then try and visualise that world we are striving for, where animals are respected and protected.