My child has Autism and SPD.
I know SPD is real. 3 years ago I was devastated when my then 3 year old child was diagnosed with classic Kanner's Autism and Sensory Processing Disorder. Often it's hard to tell which behaviors are due to the sensory issues and which due to the spectrum disorder, but through studying on the two disorders I have separated some things out. My son has tantrums that sometimes last an entire day. He doesn't like water on his head or near his ears, so bath time can be a challenge. He doesn't like to wear clothing but we are working on that. When he was younger he used to sit in the middle of a huge pile of stuffed animals and make them like a wall; no one was allowed in, that was his world, his refuge from the overload and from the many unwanted sensations of touch and noise (he would do this in different spots, always a quiet area, always on the floor or the couch where he could see if someone was coming). The rocking with his hands over his ears he still does, when noises bother him or there's too much going on. Did I mention the violence? My 6 year old, within the past year, has broken a wrist, pushed his grandmother down the stairs, tried to stab me, and hit, kicked, bitten, thrown objects, broken windows and put a hammer through my bedroom wall... the list goes on and on, the violence is astounding in one so small.
So yes, SPD is real. It's not an easy thing to live with, but just like any other disorder there are treatment options available. With therapy and understanding, and time---lots of time--- the symptoms tone down some to a more manageable level. As a mother, I wish it wasn't real, that it didn't affect my child. But it is, and it's so close I can reach out and touch it. Very frustrating disorder... hard to punish a child for behaviors when you can't help them understand those behaviors are not funny, not something to be proud of... also hard to spank a child for severe behaviors when they are immune to the pain of a couple smacks on the rump and so repeat the behaviors despite the punishment.