I used to fear blood tests...had all sorts of adrenalin rushes and used to pass out! I found what worked was to speak to the blood test nurse at my GP surgery beforehand so she knew I was anxious.

She booked me a double appointment so I could calm down after, and when I got in there she'd made up a bed for me to lie on!

Afterwards I wondered what I was worried about. It took a few seconds and didn't hurt.