answer:Pressure can fluctuate all day long. Being dehydrated effects blood pressure, and many other things. What is important is being within normal range. 99/60 is fairly common in petite young women from what I can tell. I don’t know stats, but I know a lot of women with blood pressure like that and they are fine. If it is accompanied by feeling spacey or faint, then it is something to address. Mine goes that low in the morning when I first wake, and also when my thyroid is overactive. I am spacey from it. The home pressure cuffs should be fairly accurate, especially newer ones. Next time you get your pressure measured by a medical professional bring your cuff and see if the reading is similar. Then you can have confidence in your home one.