Since you asked me in my inbox, I thought I'd answer your follow-up question here too -- if a woman's body fat goes below a certain level, she can stop having periods. I don't know if there is a stretch in between where they are just lighter, or if they suddenly stop. But that was all I could think of for why someone would start to have much lighter periods.
Have you lost a lot of weight? Sometimes that affects the period.
You should be happy your period is like that! I have no clue what would make your flow heavier??