I found out about SPD as an adult in my late 20's. I was trying to find a solution to my light sensitivity problem. I learned that Autistics often have light sensitivity problems like mine. So I contacted some Autistics on-line. They directed me to Sensory Integration Dysfunction (what SPD used to be called). It was also from those with Autism that I learned about Irlen Lenses to manage my light sensitivity problems.
I had mild to moderate, but manageable, SPD as a child. I figured out all sorts of ways to function around my quirks. My whole family is quirky so functioning around the quirks was considered the norm. However, when my Hypokalemic Periodic Paralysis got out of control in College, my SPD went from an inconvenience to a major problem. At the same time my Food Allergies also became blatantly obvious (had them from childhood, but thought my allergic reaction after eating was "normal") and much worse. It wasn't until a few years after College that I was able to first get Hypokalemic Periodic Paralysis, then Food Allergies, and then SPD diagnosed. Each was making the other worse.
Getting the Food Allergies under control, let me get the Hypokalemic Periodic Paralysis under better control, which allowed me to better manage the SPD. Additionally, getting my light sensitivity problems under control with the Irlen glasses REALLY helped lower the number of Hypokalemic Periodic Paralysis attacks I was having every day. Without the Irlen glasses around 100 attacks of paralysis/weakness per day and with the Irlen glasses around 10-30 attacks of paralysis/weakness per day.
I haven't gone a day without a paralysis attack in many years. I define a paralysis attack is any muscle of my body being non-responsive to a comand to move. I usually realize that I am having a problem when I try to reach for something and realize that that is impossible or very difficult. It affects almost all muscles of my body, including muscles that assist my lungs in breathing.
Doctors and psychiatrists don't know what to do with me so I go through periods where I avoid them completely and other periods where I ask for help from them. Right now I am in an avoidance phase. Unfortunately, I need a doctor to sign off on my medications and paperwork for insurance companies.

Kind of difficult when all your doctors dumped you because they couldn't figure out how to help me at all.