Does anybody know the symptoms if you have a folate deficiency and how serious is it?

Folate, or Folic acid is critical for cells to synthezise DNA and undergo cell division.

Weakness, headaches, diarrhea, anemia (low red blood cell count), weight loss and even psychological/behavioral problems.
Also, it is critical in the developing fetus and young children. A deficiency during these periods can seriously hamper growth and development in all spectrums.

Another important fact is that folic acid molecules are heat sensetive. Deficiencies can be found in many elderly people because they tend to re-heat a tupperware of food, eat a little bit and put it back into the refrigerator only to be reheated again and again in susbsequent days. Folic acid is effectively neutralized from the diet, and after several months of this behavior the elderly person becomes quite folate deficient.

Some meals on wheels volunteers regularly take folic acid suppelement with them when assisting elderly people on their route.

it is a deficiency in vitamin b. well, if you talk about whether it is reversible, the answer is yes. Just eat lots of animal products or take vitamins with folic acid.