I had this happen to me, and I've seen it dozens of times with other people new to longer hair. I was used to having my hair a certain length, and when it got significantly longer, I seemed to be shedding more. It seemed as though overnight I was losing massively more amounts of hair than I usually lost.
I decided to actually count the shed hairs after brushing one day. It looked as though there were 100 hairs in my brush, but I counted only 20. For some reason, when the length of my hair had doubled, it seemed that the quantity of shed hairs had looked as though they were far more than doubled. I don't know the reason for this phenomenon, but I do know that it's true, and I now know that it happens to others as well.
Fortunately, when I started my long hair journey, I had also measured my nape circumference. I was then able to also pacify myself by realizing that my nape circumference had not gotten smaller.
If your hair is long enough to make a ponytail at the nape, I suggest that you also measure your nape circumference, just for the occasion that you think you're having a major shed. If the back of your hair is long enough to measure, but the sides are not, then measure again when more and more hair can fit into a ponytail.
If you cut bangs or face-framing layers, then do take another new measurement, as your circumference will naturally be smaller without the inclusion of the bangs or face-framing layers.
Almost everyone thinks at some time or another that they're having a major shed, when they're really not. They look in the shower and think there's an awful lot of hair there; more than there used to be, or like me, they see more hair in their brush. In truth, it's just more quantity of hair due to length, not more hairs.
It's really good to have a baseline measurement to be able to go to in order to determine whether or not there is really a problem.
Also remember that on average, we do shed about 50-100 hairs per day. That is completely normal.
On occasion, people do shed a lot of hair. For example, most women are familiar with the post-partum shed. That is extremely common and it did happen to me, especially after the birth of my second child. However, the hair started growing back almost immediately. Sometimes after a trauma or a really severe stress, people can have a larger than normal shed. Again, this hair grows back right away. While it's frustrating to have temporarily thinner hair, it's nothing to worry about, if you can feel or see new hairs growing in. It is worth checking with the doctor though, just to be on the safe side.
However, if you really are having a big shed for no reason that makes sense, and if your hair's circumference is significantly reduced, please see a doctor, as soon as possible. Problems with thyroid are a common cause of hair loss. Also, there can other hormonal issues at play. Most of these problems can be treated, and this will save your hair, but much more importantly, your health.
Do remember though, that most of the time, as your hair gets longer, you will hit a certain length where your hair seems to be shedding more, but it's just an illusion. So do measure that circumference. It may give you peace of mind.
On another note, I am feeling a bit more chipper and cheerful today, and I hope to post some hairstyle photos and/or a video later in the week. The weather may be ushering in some migraine-free days, which I'm looking forward to very much.
Love to all, my friends. 'Til tomorrow.