Now, this is probably something that gets asked a lot around here, but I'll ask anyway.

Two hours or so ago I lay down with music on, my intention was to reach SP.

After some time, not sure how much, I got this itch on my nose, which is not very unusual, and I thought nothing of it. Then all of a sudden this itch increased in intensity tenfold and became almost irresistible. I thought to myself: "This is it" and endured it. All of a sudden I feel a buzz going over my face and body, which lasts for a couple of seconds, then my heartbeat slows down but becomes a lot stronger, like someone beating on the inside of my ribcage with a hammer. I manage to stay calm and composed, and eventually my heart calms down.

After this though, even though I felt different in general, I didn't feel any more effects. I decided to risk it all and try to sit up and see if I was in fact in SP or not, and it turns out I wasn't.

What did I do wrong? What can I do different the next time?