Well, I have an MD in the household. But I get anxious when measuring blood pressure because I'm scared it will be to high. My dad has it, and I'm always afraid I'll get it too. When she ambushes me and measures it when I don't have the time to panic, it is usually fine.
On the other hand, I had a regular blood test several weeks ago, and my blood sugar was borderline high for a fasting period. I just went out and bought a glucometer and tracked it for days later, it was much lower. It just happened on that one reading at the lab. The only explanation is that I was fasting for too long (close to 16 hours) and the lab was not the first thing I went in the morning, I had one more place to visit before. So my body was already fully woken up and/or my liver started doing its thing and produced glucose from fat or whatever.