When it comes to hair loss, should I also consider the change of hair becoming thinner as important as the hair falling out?

Lately, the amount of hair falling out when I wash it doesn't seem much different from before, but my hair feels like it has gotten thinner overall.

Especially when I tie my hair up, it seems like the ponytail is smaller than before, so it bothers me for no reason.

When people think of hair loss, they usually start by thinking about the amount of hair falling out, but I would like to know if a decrease in hair thickness is actually a significant change as well.

I am also curious about what areas I should look for to check for these changes before they become noticeable.