8 Weeks 4 Days No Heartbeat?

I had an ultrasound done about alil over a week ago and the heartbeat was very strong and the doctor told me that since im lil more then halfway through my pregnancy and the heartbeat is 158 that my chances of miscarrying were slim.. yesterday i went to my friends birthday/grad party and i was feeling sick.. so i went to the bathroom and threw up.. then i had to use the bathroom and when i sat down i seen red spotting, then when i wiped i had a dark clot and i freaked.. i also had some cramping too.. but i dont soak a pad its only when i wipe now.. my mom took me to the hospital.. they did a urine and blood test.. said the blood test for the hcg levels were high * but at the end of the visit said they will go down which i dont see how thats possible when they keep goin up instead of down * and when they done an ultrasound, the lady left the catheter in * last time the lady that done my ultrasound took it out * and then left it in my area and said she was goin to get the ER doctor and he came in and looked too and then came by my side, started rubbing my forehead saying its not my fault, things like this happen, then said the dreaded words that i knew were coming cause i started crying when she left the room for the doctor and said they couldnt find a heartbeat and i lost it.. they gave me zanex to help me sleep but i still got up through the night and morning crying, asking god for the heartbeat back and id do anything for it to come back.. i dont get how i can have a strong heartbeat about a week ago, and then it disappear.. im so devastated and they wanna do a D&C monday if it doesnt pass through.. but i just dont understand how the heartbeat was sooo strong and everything was fine then it just dies? someone please explain this to me, cause im losing my mind and i cant sleep even with the medication :(