Hello~I think you symptoms are due entirely to anxiety, I know when I am in a high state of anxiety, I can't breath and my heart does all kinds of strange things. Also, due to the amount of Adrenalin being released when stressed, your legs can and will feel heavy and even rubbery at times; that is why they get better when you rest. The sudden jolts out of a sound sleep are also usually stress related.
I really don't think it is a blood clot, especially at your age, that would be pretty rare.
I have a blog on my home page all about the symptoms of anxiety, you are welcome to have a look at it, you will be surprised at all the things stress/anxiety can do to the body.
I hope you feel better soon, God bless you.