Everyone experiences altered states of consciousness.
You might not realize it, but when you fall asleep, you pass through many different states.
When I first started meditating at night, I didn't really notice anything special. I would relax my body, clear my mind, and promptly fall asleep.
But with practice, you can slow this process down. You can watch yourself fall asleep. You can watch yourself start dreaming. You can see the dream materialize in front of you, and become your new reality, in one continuous experience, never losing consciousness.
You can do the same waking up. You can take your time, and watch yourself go from a dream world, to laying in bed, to full wakefulness, without a break in consciousness.
If you take the time to learn this skill (and it is just a skill, like anything else), you will begin to notice that dreaming isn't your only option. There are other places you can go.
I call this the map. Just like an explorer, you can fill out your map, and discover new destinations, in your own mind. Some places are easy to get to, but some are very hard, and take a lot of careful mental movement.
I call this process of exploring your mental map surfing.
When I was younger, I wanted so much to have an out of body experience (OBE). I read books during the day, and meditated every night, for six months straight. I tried so hard.
Finally, out of exhaustion, I took a break. That morning I had my first out of body experience, while waking up. Here's what I wrote about it, years later:
I can remember dreaming that I was on the side of a road. I started to wake up from the dream, and my vision went from normal dream vision, to myself lying in bed. As I was lying in bed, I was very relaxed and bored. I started playing with my arm - it would float up, then I would pull it back down. Then it would float back up, and I would pull it back down. After about 30 seconds of this, I realized that my arm shouldn't be floating upwards!
I don't think it's a coincidence that my first OBE happened when I finally took a break.
You need to be in a somewhat playful, somewhat bored, somewhat passive state of mind. Not so passive that you don't care – you should be relaxed, calm, and willing to see what the universe gives you, without judgement, and without forcing anything.
This is why I call it surfing.
You are playing an active role – you are doing something physical, that you trained for, in order to have a cool experience. But you need to relax. You need to ride whatever wave comes at you, on your map.
Enjoy the ride, and if you fall off your board (and lose consciousness), don't sweat it. Maybe you'll wake up and have more opportunities to surf, maybe you'll have a fun dream, or maybe you'll just sleep deeply. Enjoy every outcome, for what it is.