There were six months gap in my period. It started again four days ago. The flow is heaviest heavy I would say. But I noticed I had a drastic weight loss in such a few days. Given that I have stopped exercising and eating lots more than usual. Is it norma

Not normal. Several cause. You can wait and see if your periods resume normally in next 2-3 months. If not look for cause which could be female hormonal low thyroid or may be PCOS. Have gynecologist evaluate you. At your age it is not normal to miss periods for 6 months.