Hi, I am so sorry to hear you are going through this. I've had a similar experience, sorry for the lengthy post but I found reading others stories helpful...
I am nearly 18 weeks now, we too had a cystic hygroma discovered at the 12 week scan. Measured 4.7mm and then 4.8mm when we had CVS 4 days later. They also said they could see skin oedema but no other fluid around any organs etc which is apparently a good sign. My antenatal bloods showed low HCG and pappA which when re-adjusted (they got my ethnicity wrong) weren't so bad but still low.
We were given a 1 in 28 chance of Edwards/pataus and 1 in 61 chance of downs syndrome. I was prepared for the worst. After 3 days found out the trisomies were negative and after an agonizing 3 weeks found that the array CGH was normal.
Then had a scan and appointment last week and the fluid had gone - although I find this reassuring apparently it doesn't mean anything with CH, nor does the amount of fluid (unlike raised NT) - I'm trying not to Google anymore. Having said this, they couldn't see anything obvious on the scan to cause concern. Need to wait for 20 weeks to rule out cardiac problems for sure, then 4 weekly scans to check everything growing as expected.
So, yes, it's terrifying I won't lie and we are not out of the woods but with each subsequent test result we feel a little more hopeful. Everyone has their own coping mechanisms but I'm trying my hardest not to stress too much as it won't change the outcome. This is easier said than done. I found reading stories on here both good and bad helped. I really hope you get reassuring results and I'll be thinking of you. I truly believe this is one of the hardest things to go through and the wait is dreadful x