When I listen to paraliminal I sit on a chair but after some time I feel so sleepy that I can not listen to the voice carefully and thus I do not understand it. I feel so drowsy. Is it a problem?
That's normal. Don't worry about listening too hard. The two voices on the Paraliminal overwhelm the conscious mind and talk directly to the non-conscious mind. You'll often feel like you've fallen asleep. As you wake up at the end you can know that your mind has been listening and following the instructions.
