Hey there, first of all welcome to DV

One thing that may be stopping you, when you say you get anxious and your heart beats really fast? This may be you getting excited about SP, one thing that can cut out SP is you thinking too much or getting excited. Try to relax and not think about your body at all.

Have your eyes closed, it'll help you relax and enter SP quicker id say.
When you have SP, just let it take you for a ride, go with the flow and soon you will be in a dream.

Good luck!