The normal range of haemoglobin for a man is 13.5 to 17.5 g/dl and for a woman is 11.5 to 15.5 g/dl
Are you sure that the level of haemoglobin is 6.4 ?
Age and sex?
she might have checked- hemoglobin A1c test.
The hemoglobin A1C test is a valuable measure of the overall effectiveness of blood glucose control over a period of time.
In patients with poorly controlled diabetes, this level is 8.0% or above, and in well controlled patients it's less than 7.0%.
For people without diabetes, the normal range for the hemoglobin A1c test is between 4% and 6%
Also Kidney disease and liver disease may also affect the result of the hemoglobin A1c test. This has resulted in the fatigue and tired feeling
My opinion is that,please make an appointment with doctor, so that appropriate management is adviced
i wish for your good health.