I agree with remar 100%. And, yes, a BP can dramatically vary, from second to second. It is affected by things such as stress, anxiety, caffeine, sleep cycles, etc.
If you find yourself being obsessed with taking your BP, and feeling anxious about it, you need to mention that to your doctor. Sometimes the very thing meant to help, causes us harm. That might be the case with you too. You may be overthinking it, and overly focused on it, which is mever good.
You need to have more time in between readings to get a correct one. If you take it within a couple of minutes of the last reading it can be false. You might want to try taking it around 15 minutes apart.