What is alopecia? How to detect it?

I am dealing with a huge amount of hair loss these days. I am concerned about; whether I am dealing with the hair loss disorder called alopecia. For a few months, I can see unusual hair loss everywhere around my house. I find a large amount of hair on my pillow, in the shower, on sheets, on my hairbrush, etc. I still haven’t developed any bald spots, but my hair density, and decreased a lot. Could it be alopecia? I have tried various hair loss remedies, and nothing has worked. Can someone here please suggest something? I am really worried.
What is alopecia? How to detect it?
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