How could we, in two weeks, go from a heartbeat of 149 to nothing?

It was a very normal pregnancy. Strong HCG levels throughout. We heard the heartbeat at 8 weeks. It was 149 and baby was measuring correctly. I'd never once had any spotting throughout the 10 weeks. Then cramping started around 7 PM on a Thursday night. [read other miscarriage stories or more about miscarriage at 10 weeks]

I didn't think too much of it, thought maybe it was gas or something. The cramps kept coming throughout the entire next day. Around 3 PM on Friday I started having a brownish discharge and it was kind of like a light flow during the start of a period.

I called my OBGYN and spoke to the nurse. She told me it could be dehydration causing the cramping and my body could just be cleaning out old blood, but it could also be signs of an early miscarriage. She said if my discharge turned light pink then red I should go to the ER.

After getting off the phone with her my discharge didn't change color but was a steady flow to the point that I had to put a pad on. I called my husband and said we need to go to the ER. I had this intuition that something was wrong.

I walked in crying to the ER telling them I needed to hear my babies heartbeat because of the symptoms I was having to know it was ok. It was the longest 4 hours ever in an emergency room. They took a urine sample, blood and eventually an ultrasound, but of course, we had to wait for a doctor to tell us the results. 

My HCG level was 19000 so I thought great the baby is probably fine. I was wrong. The doctor came in and squatted next to the bed with a grim look on his face. My baby had no heartbeat. How could we, in two weeks, go from a heartbeat of 149 to nothing??

He diagnosed me with an incomplete miscarriage and sent me home with pain pills. Telling me I'd pass the baby in the next few days and to follow up with my OBGYN.

I still can't believe it. I cry randomly about it and just can't fathom what went wrong. Praying for my lost baby, myself and my husband. I am lucky to have lots of support around me, but it just isn't easy.