You might consider taking your BP with another machine.. some are more accurate than others. A manual is usually better... drop into your doctors office I am sure they would do it for free.
Anything below 90/60 is considered a s low BP, but it is not usually treated unless it is consistently that low or causing symptoms such as you describe. This is not a serious condition, in fact low BP is much better than high BP in an otherwise healthy individual.
You should see your doctor and let them check your BP. One reading is not enough to make a diagnosis, let you doctor get involved if you feel light headed or dizzy. You can look at my BP tracker here and you will see that my BP is on the low side of normal and will occasionally drop below 90/60 and I'm fine with that. Also, if your symptoms are extreme, be careful about driving.
Jon