Symptoms: cold sweat, dizziness, nausea during and after period. period lasted 7 days was heavy until the last two days and very dark almost brown ?

Most likely, normal: Rule out pregnancy, of course. My own take on this is that, particularly with heavy menses, there is notable amount of retrograde menstrual flow (back flow of menstrual effluent) through the fallopian tubes into the abdominal cavity. This could serve to irritate the peritoneal lining (eliciting pain, bloating, etc..) as well as nearby bowel; leading to some of the GI symptoms described.