Just wait (if you're a woman who plans on having kids) shortly (a couple weeks-months depending on your body's hormones) after giving birth, you'll be thinking all your hair is falling out.
During pregnancy your body extends the growth stage (hair= mostly in growing stage, ~10% in resting stage, after resting stage it falls out, online says most lose about 100 hairs a day), post pregnancy all those extended growing ones flip over to resting then falling out, so just as you're sleep deprived, nursing, emotional, and super insecure about your post pregnancy body a lot of hair, oh-so-helpfully, decides it's time to come out in what seems like handfuls, every day until you're back to where you would have been if you had continued your life non-pregnant.
During pregnancy your body extends the growth stage (hair= mostly in growing stage, ~10% in resting stage, after resting stage it falls out, online says most lose about 100 hairs a day), post pregnancy all those extended growing ones flip over to resting then falling out, so just as you're sleep deprived, nursing, emotional, and super insecure about your post pregnancy body a lot of hair, oh-so-helpfully, decides it's time to come out in what seems like handfuls, every day until you're back to where you would have been if you had continued your life non-pregnant.