Hypotension, which is, strictly speaking, a physical finding rather than a disease — can be abnormal and can lead to death quite rapidly if it is due to a heart attack, a major hemorrhage, or something like that.
However, hypotension is usually secondary to some condition, be it one of those above, or severe dehydration following diarrhea or high fever. In a healthy walking and talking person, there is no blood pressure that is too low and that would be diagnosed as a disease. When I practiced in Cambodia, it was quite common for me to see healthy Cambodians with blood pressures of 80/60, a level that in this country would be labeled hypotension.
The famous Met Life database, used for years to assess mortality against blood pressure, shows a smooth reduction of mortality with lower blood pressure, meaning it is always healthier to have lower pressure. The myth of someone having “low blood pressure,” as in disease, probably comes from nurses and doctors unfortunate comments when taking a person’s blood pressure, along the lines of “you have really low blood pressure” or “do you feel OK, your pressure is really low?” thereby convincing the poor patient that they have a disease.
Having said all that, there are a couple of uncommon conditions which lead to such low blood pressure that the person faints when they stand up. Low blood pressure is always more symptomatic when a person stands, since the pressure necessary to get blood up to the brain must increase. If it cannot increase, as in diabetic autonomic neuropathy, or a rare disease known as Shy-Drager syndrome, or simply from dehydration, then symptomatic hypotension causing dizziness and fainting will occur.
Many normal people have a brief period of dizziness when they stand up. This is orthostatic (relating to the upright position) or postural hypotension. It is not abnormal and does not lead to any pathology. People with blood pressure in the lower range do not necessarily feel cold, nor are people with high blood pressure hotter than normal. The level of the blood pressure has no relationship to resistance to colds or other infections.