My friends blood pressure is 85/45. Is that too low?

drink more water
be happy that it is low rather than high
see a doctor to understand if the readings you have are a problem
If you are feeling dizzy and friends say that it is your blood pressure with out a test, the problem could very well be blood sugar problem so seek medical advice from a doctor

Mayo clinic says: Most doctors consider chronically low blood pressure too low only if it causes noticeable symptoms. (Such as dizziness, especially when first standing up). Some experts define low blood pressure as readings lower than 90 mm Hg systolic or 60 mm Hg diastolic - you need to have only one number in the low range for your blood pressure to be considered lower than normal. I hope this helps!

health problems
internal bleed
dehydration
see your doctor now to get a proper diagnosis

That paper coined a new term, "isolated diastolic hypotension," which refers to a low diastolic blood pressure (less than 60 mm Hg) and a normal systolic pressure (above 100 mm Hg). Older adults who fit those conditions are at increased risk for developing new-onset heart failure, the researchers found.17 May 2015

UAB - The UAB Mix - Diastolic blood pressure: How low is too low?

https://www.uab.edu/mix/stories/diastolic-blood-pressure-how-low-is-too-low Low diastolic pressure for what reason Google Search

low blood pressure dangerous only if it causes
noticeable signs and symptoms, such as:
Dizziness or lightheadedness
Fainting (called syncope )
Dehydration and unusual thirst - Dehydration can sometimes
cause blood pressure to drop. However, dehydration does not
automatically signal low blood pressure. Fever, vomiting, severe
diarrhea, overuse of diuretics and strenuous exercise can all lead
to dehydration, a potentially serious condition in which your body
loses more water than you take in. Even mild dehydration ( a loss
of as little as 1 percent to 2 percent of body weight ), can cause
weakness, dizziness and fatigue.
Lack of concentration
Blurred vision
Nausea
Cold, clammy, pale skin
Rapid, shallow breathing
Fatigue
Depression
Low blood pressure can occur with:
Prolonged bed rest
Pregnancy - During the first 24 weeks of pregnancy, it's
common for blood pressure to drop.
Decreases in blood volume - A decrease in blood volume can
also cause blood pressure to drop. A significant loss of blood
from major trauma, dehydration or severe internal bleeding
reduces blood volume, leading to a severe drop in blood pressure.
Certain medications - A number of drugs can cause low blood
pressure, including diuretics and other drugs that treat
hypertension; heart medications such as beta blockers; drugs for
Parkinson's disease; tricyclic antidepressants; erectile dysfunction
drugs, particularly in combination with nitroglycerine; narcotics
and alcohol. Other prescription and over-the-counter drugs may
cause low blood pressure when taken in combination with HBP
medications.
Heart problems - Among the heart conditions that can lead to
low blood pressure are an abnormally low heart rate
(bradycardia ), problems with heart valves , heart attack and heart
failure . Your heart may not be able to circulate enough blood to
meet your body's needs.
Endocrine problems - Such problems include complications with
hormone-producing glands in the body's endocrine systems;
specifically, an under-active thyroid (hypothyroidism), parathyroid
disease, adrenal insufficiency (Addison's disease), low blood
sugar and, in some cases, diabetes.
Severe infection (septic shock) - Septic shock can occur when
bacteria leave the original site of an infection (most often in the
lungs, abdomen or ******* tract) and enter the bloodstream. The
bacteria then produce toxins that affect blood vessels, leading to
a profound and life-threatening decline in blood pressure.
Allergic reaction (anaphylaxis) - Anaphylactic shock is a
sometimes-fatal allergic reaction that can occur in people who are
highly sensitive to drugs such as penicillin, to certain foods such
as peanuts, or to bee or wasp stings. This type of shock is
characterized by breathing problems, hives, itching, a swollen
throat and a sudden, dramatic fall in blood pressure.
Neurally mediated hypotension - Unlike orthostatic
hypotension, this disorder causes blood pressure to drop after
standing for long periods, leading to symptoms such as dizziness,
nausea and fainting. This condition primarily affects young people
and occurs because of a miscommunication between the heart
and the brain.
Nutritional deficiencies - A lack of the essential vitamins B-12
and folic acid can cause anemia, which in turn can lead to low
blood pressure.
Severely low blood pressure can have underlying causes that may:
Be an indication of serious heart, endocrine or neurological
disorders
Deprive the brain and other vital organs of oxygen and
nutrients, ultimately leading to shock, which can be life
threatening