Thick blood is an actual medical condition. It's pretty rare, but I did have a co-worker w/ it. He had a rough time. I'm sure they will be able to tell if you have this during the testing they are doing. Hopefully you don't have it though!
http://www.nhlbi.nih.gov/health/health-topics/topics/poly/
This site has good info too:
http://www.livestrong.com/article/5984-need-thick-blood-disease/