Blood pressure low?.............?

Okay, so my blood pressure fluctuates during the day which i know is normal for everybody. but for the past two weeks its been quite low. I started a new placement on a ward and in the mornings i always feel huge pressure on my chest, sickness and like i'm going to p out. ..I had a blackout about a week or so ago n got really clammy and almost threw up twice. My BP has been mainly in the low 90's for systolic (top number) and mid 50's to low 60's for diastolic (bottom number). I'm quite worried as ive also been feeling dizzy as if i have been drinking and always thirsty...even though i'm drinking plenty of water. i know this is a sign of diabetes though i got tested a few years back and was told im not diabetic. My question is how low does your blood pressure have to be to be considered dangerously low enough to see a doc? ...also, any idea's on what could be causing this?