There are certain changes happen in your body and mind when you sit in meditation. While your eyes are closed, the energy which was suppose to be for your eyes to have a physical level of vision; the same energy gets utilized for inner vision. Your physical eyes are capable of looking the physical world but you can only use it to a certain extent. However, when you start using the power of your inner eye you can have another level of experiences. Different people can have different experiences in that, some people might see the universe, some might be able to hear the sounds or some might be able to see different colors or light patterns.
In fact your brain is a blue print of this whole universe. You can say, your brain constitute of all the mysteries of not just the universe we know but infinite universes. When you start getting deeper and deeper in your meditation, the mysteries of all the universes start revealing themselves in front of you. Layer by later you start to have a more clear understanding of your existence. Whatever experiences you gain during your deep meditative state are due to the power of your mind. Means they are just part of your mind itself. However this is just the beginning stage in revealing of self. There are more layers to uncover while you go further deep.