Hi Theerapun
It's a pleasure to help.
When meditating be more an observer of the thoughts, than the thinker, but it's okay to let your mind wonder.
You can expect to feel very relaxed and more on the happy side.
Your falling asleep was due to both having 4 hours of sleep the night before, and listening to low theta entrainment - your brain said, "Here's my chance let me take it!", to the opportunity to get some rest induced by entrainment.
Meditation is normally associated with calm reflection, stillness and inner quietude. It is possible to reach states of blissful tranquility through meditation.
Some other states associated with 4hz-7hz brainwaves are recall, fantasy, imagery, creativity, planning, dreaming, drowsiness, and ESP.
Enkephalins, Endorphins having opiate qualities (effects like morphine) are stimulated at 4hz, which is the level that the meditation(deep) drops to.
Enjoy!
