Hi @anonymousgirl , some variations in period cycles are expected during periods of stress during exam periods for example, however they shouldn't be less than 21 days or more than 35 days on a regular basis, and there shouldn't be large variations (>2 weeks) between your longer and shorter cycles. These would be features that require further assessment and potentially investigations to rule-out possible causes such as thyroid disorder or polycystic ovarian syndrome (PCOS).

You may not have anything to worry about based on your cycle and that one-off incident alone, however given the accompanying thinning of hair, you would benefit from further assessment to be assured that there are no underlying reversible causes such as thyroid disorder. I would recommend for your to speak to your parents about this and arrange a review with your doctor for a more detailed assessment. I hope this helps!