Extremely fast heartbeat/ Heavy Breath / Exaggerated shaking

So a few months ago I attempted a lucid dream, I am very new at this so I had no idea where to start.

What I did was put on ambient calm music, and got into a position where I would be comfortable for the next 40 minutes (was laying straight with my arms by my sides). I kept trying to keep my mind busy, thinking of shapes and basic geometry, and imagined this red dot in my mind that I was focusing on. I also kept breathing in a specific rythm, keeping my breath somewhat deep but moderate.

Soon after, I began losing feeling in my legs, then my hands, and this weird balance between consciousness and unconsciousness came to me, I opened my eyes and looked into complete darkness (lights were off) and closed them again, thinking I was still awake, and kept focusing.

Soon after, I felt as if I was being pulled into a black hole. I felt I was sinking more and more, quickly dropping towards a center with the darkness literally pulling itself over me. I was both frightened and excited, and I felt as if my heart started raising. After approximately 15-20 seconds of this, my heartbeat was through the roof, I exercise 4-5 times a week and I never get anywhere as close to this, I´m ballparking a 185-200 BPM (I´m 19 and very healthy.)

Soon after, my eyes felt as if they were rolling around senselessly, and I started breathing very heavily. I was sweating, and I forced myself to wake up. My arms were very heavy to move to begin with, aswell as my legs, but once I got movement again I started shaking excessively, I felt terrified, It was literally the scariest thing I had ever done, and I´ve got a pretty tough bucket.

Have anyone else experienced this? Do you have any tips for me to improve myself in these practices? Also I apologize if this is the wrong section to post this, but once again, I am very new here.

It can also be worth mentioning that I had also read prior to my attempt that you can be paralyzed and pretty much tortured mentally, I was most likely fearing that this would happen and aborted.

Thank you!

Hm.. Well,first we start at the end I feel ? You won't be tortured,or paralyzed for this purpose. Paralysis is common to experience at some point,but as many members here can assure you,they aren't anything to fear,and can actually be made pleasant. This might seem odd,but congrats on your progress. Lol The only time I've had anything remotely similar to this occur,was before my first lucid dream,and I feel that I felt unsure in the whole process. Whether it was real,whether I would astral project by mistake,etc etc. and so my body sort of fought the process. What I would suggest,is actively directing your wild into a dream once you approach the moment you refer to as "pulled into a black-hole",by trying to move(use) your dream body,as you may already be in a dream,which your fears and things are shaping. Or trying to imagine a dream scene. Hopefully this helped abit.