Well according to the American Heart Association:

Normal = less than 120 systolic and less than 80 diastolic
Prehypertension = 120 – 139 systolic or 80 – 89 diastolic
(Hypertension) Stage 1 = 140 – 159 systolic or 90 – 99 diastolic
(Hypertension) Stage 2 = 160 systolic or higher or 100 diastolic or higher
Hypertensive Crisis = Higher than 180 systolic or Higher than 110 diastolic

It's important to find out the cause of it, if it is a lot lower than normal and causing symptoms.
Some people can have low BP numbers and no symptoms (athletes for instance), and so i agree that sometimes the numbers need to be ignored, but if there are symptoms then the numbers matter.
For 18 months i have experienced days of constant dizzines, even while laying down or sitting, coupled with fatigue, nausea and have experienced shock episodes.
My B.P is rarely higher than 75/55 and i'm still at a loss as to why it is so low.
I've been eating Celtic Salt and Himalayan salt for 12 months now and it doesn't change my symptoms or BP readings at all.
I'm in the process of chasing the rabbit down the hole regarding all my symptoms and getting closer to 'why' the BP is so low.

Really try dosing heavy with salt...it's not bad for you with LOW B.P. table salt has many fillers and additives to stop it condensating and turning into a solid mass...best to avoid that stuff...that is BAD! The reason we're lead to believe salt is bad is due to the media because convenience food is loaded with salt rendering most of the population with HYPERtension, so the message for THEM is 'Salt is bad'. Salt is essential for life!
Low BP is not that common, if you read the Mayo Clinic's website they talk about high BP and dismiss completely mentioning low BP!

Himalayan and Celtic salt both contain excellent minerals...over 80 minerals coupled with raising sodium levels.
That works for many people on here with low BP and adrenal issues. Also licorice is another remedy for boosting BP, again something which i've tried and it hasn't helped me personally yet has helped others on this forum.
If you've made it your mission to avoid salt in food due to believing it's bad for you, your low BP might be as simple as a sodium deficiency. You should notice a difference quite quickly if you consume salt IF salt deficiency is your issue.

If the salt doesn't change your numbers and symptoms persist, some diagnostics are needed to figure out why your BP is dropping. Viral attacks can cause low BP, as well as severe adrenal function issues.