So you get tired and you lay down, and you close your eyes and and your mind wanders. Then, strange thoughts and images begin to get into your mind. Not bad things, just things that didn't really come from your own mind. You go into a daze. You get more and more of these foreign thoughts until you snap awake.
What just happened? You're suddenly thinking of something that wasn't part of your own thought process.
Now, try doing it differently. When you're tired, lay down and leave your mind clear. You'll get subtle images or sounds that you didn't purposely come up with. Pay close attention to them. The trick is to concentrate. Sometimes it's gibberish, sometimes it's neat stuff. Now, after a moment you'll take these thoughts and start building on them, imagining them in different ways on your own. But then the 'connection' is gone and you're no longer receiving thoughts, but coming up with your own. Now it's just your imagination. Well, clear your mind again. Wait for more stimuli to appear. It's regular to connect and disconnect a few times. You're just warming up.
If you keep going, you start to slip in deeper. Concentrate an everything you see and think. It becomes harder to pay attention because more information is being thrown at you. It's a lot of stuff - sometimes many visions at one time, and many sounds. You lose awareness of your body, and now the data is everything. This is where a person normally goes into a complete daze and loses coherence, waking up later and forgetting what just happened. But you don't have to do that. You can keep going. Treat it like television - notice all the channels but focus on ones that interest you. You can ask questions, too. You won't always get an answer, but you often will if you keep trying. Don't let yourself imagine answers, just watch and wait for the information, and focus on everything you see there.