Hi, you experienced something called sleep paralysis, I had this 4 times when I was in my early twenty's, Each time was different and got more terrifying as they went on. Its been 30 years since I had them, yet I can still remember the absolute fear that accompanies these attacks. Also I will never forget the dark shape of someone/thing rising through my bedroom floor.
Apparently only about 8% of people experience this, some get it for years, some only the once (but once is enough) there is a lot on the web about this, just google it.