When the second number (usually the lower one) is elevated that means
the blood vessels are constricted all the time --- this puts pressure on the heart when it contracts, and can lead to heart failure, or aortic aneurysms.

The upper number goes up with activity, after a hot bath, when upset, with age (with hardening of the arteries), and reduced kidney functions.
The systolic can vary all day long...higher in the morning, lower at night. Caffeine, drugs (stimulants--certain antidepessants like Effexor/Cymbalta) can also affect/raise systolic.

The diastolic varies less with situations. It has only been recently that systolic pressures are being treated more aggressively now. In the past a "certain" elevation was accepted for the elderly. There are people with very high diastolic numbers with not so high systolic ones. Like 150/100.

Blood pressure can elevate with pain, stress, eating, sex, illness, all sorts of activities. It is always a good idea to keep a log, showing daily variations.
Many people show higher pressures in the morning, (when cortisol is highest) and lowest while sleeping (this is called dipping). Some 20% or so people do not dip while sleeping...so there are special treatments for non-dippers.
People who "dip" alot and take blood pressure meds besides can get seriously low pressures during sleep, which can impact the brain and retina. That is why blood pressure meds are usually taken in the morning.

The autonomic nervous system also has effects. For an anecdotal example:
Anticholinergics, lower my blood pressure dramatically. If I use Levsin for my GI issues, (which I don't often), I have to lower my Blood pressure meds.
I've had diastolics go to 60 on Levsin. Which is very odd...but it happens for me. So something unique is happening there for me!!! That is to keep in mind, since people vary tremendously with blood pressures..Some very labile, others very stable.