At about age 32 I had a somewhat similar experience to what you have had - without the shaking.  I'll tell you a little about it and then offer my thoughts about it.

As I was falling asleep one evening I felt myself descending down into a deep, dark, and bottomless pit.  I consciously knew that if I continued down the shaft of darkness, I would die.  I forced myself to wake up and felt my heart racing and my breathing very difficult.  I was frightened to go to sleep 'ever again' - and often times I would awaken with a jolt just after dozing off, with the same symptoms, but without having experienced the descent into the black hole.  At that time I was under a lot of physical and emotional stress in my life.  I was attending college full time (even with extra credits to get through quickly) with a wife and two children, while unloading box cars on graveyard shift two and three nights a week.  The sleep symptom of awakening with a jolt and racing heart and difficult breathing stayed with me for a few years, though it did get better.  During that time I had a fear of going to sleep.  I also had panic attacks from my early years up to and through that time too.

Not too long after college and with a good job, nice home and family, I found myself very unhappy with life and began a search for who I am, not knowing that's what I was doing.  I eventually found meditation, a type that reflects inward and searches the soul.  Even with a couple of years of practicing this - which was bringing me more peace than I'd ever experienced before, I would still awaken in the night in panic with heart pounding and one time I was so frightened that I called an ambulance and paid a visit to a hospital where I was kept overnight and they could find nothing wrong with me. Yet, that didn't solve the problem.

Eventually, after getting glimpses of intense abuse from a close relative and denying to myself that it ever happened, I hit PTSD.  PTSD so intense that I was physically re-experiencing the abuse - constantly.  There was no denying it any more.  By now I was divorced, retired, and living alone.  I went into such intense fear that I kept my door locked 24/7, moved my computer and a comfortable chair into my bedroom, and lived there for the next  six months going out only to cook, get groceries, and eventually do some counseling.  I could sleep for only 20 or 30 minutes at a time before being awakened with horrible nightmares.  I was suicidal but had to lie about that to prevent "caregivers" from giving me medication that I did not want to receive.  It was the most devastating era of my life and I have been through things that most people would think were far worse, but they weren't.

I have eventually healed all of the trauma around my abuse and no longer experience either the awakening in the middle of the night or the panic attacks.  Counseling really wasn't all that beneficial, but staying on course with my meditation was.

My earliest memories from childhood are nightmares.  I have had nightmares/"bad" dreams all my life until the PTSD subsided.  I had panic attacks forever.  I was in constant fear.  Basically fear of living.  The changing moment in my life some 35 years ago was when I learned for the first time in my life that unless "someone is pointing a gun at your head - fear is irrational."  It happened during a seminar on Transactional Analysis that I first learned that, and that is what started me on my journey.

If you have fear, or panic attacks, or the sleep pattern you are describing - it isn't all what's within your body.  What we dream, whether it is a nightmare or luxurious harmony, it is what you as spirit are working on in life.  Dreams are from your Higher Self, or your Inner Self, or from God, whatever you choose to call it.  Listen to those dreams and try and determine what the messages are.

Besides the physical, I would suggest you pursue the spiritual.  When I say spiritual I don't mean religion, though that can be a help too, but what I do mean is that you are spirit residing in a body and you are in a constant learning process.  Learn what spirit is telling you and try to learn the message from within.  What you do may be meditating, it may be prayer (two way communication - not just one way), it may be learning all you can about what you are dealing with (as I believe that you are doing), it can be dozens of things.  But keep in mind that you are neither insignificant, nor are you here to suffer and that in the eyes of God everyone is equal.  The journey will have both peaks and valleys, but as you face the valleys the rewards far exceed just sitting there doing little about what you're dealing with.

Best to you in what you discover on your path.