My suggestion is a visit to your Doctor.
I occasionally get low readings (never with any obvious effects) but always, I take three or four readings to find an average - for me that is very successful.
For you to have a (single measure?) low reading enough for a recognised symptom of dizziness - in your case collapsing to occur, is something you don't want to be alone with.
Sudden, albeit random, low measures require an explanation if there is one, and as Sheryl mentioned, maybe a medication adjustment will help!