Some of the causes according ayurveda are :

Not having enough food, let's say fasting.
Doing sex on an excessive rate.
Taking spicy food on a regular basis.
Foods which are penetrating in nature like ginger when consumed.
Undergoing heavy exercise and exertion.

Symptoms include:

A bleeding for more than 7 or 8 days.
Having increased quantity of blood loss during the menstrual cycle. For example, soaking through one or more sanitary pads or tampons every hour for several hours in a row.
Need to change the pads at the time of night due to heavy flow.
Due to the heavy bleeding the daily activities are disturbed and have to bring a change in them.
Spotting in the periods.
Feeling pain or cramps in the lower abdomen.
After crossing the menopause period when your vagina still bleeds at some times.

Signs of anemia are seen if you lose so much of blood hence heavy menstrual bleeding is not at all normal. Having less amount of iron in your body is the situation called anemia, which when remained untreated can be dangerous for life.

A menstrual period which is prolonged and continues with extremely heavy bleeding. And here the heavy bleeding is not just some increase in blood outflow but it is as heavy as you have to change your pad every hour or more.