I have been searching for an answer to this question for years and someone pointed me in the direction of this site. I have never been diagnosed with SPD however I am suspicious. A bit of background: I have an anxiety disorder with panic attacks which I predominantly triggered by motion which causes dizziness. It's a viscous cycle.
It started when I was 16 and took some travel tablets when going on an overnight boat trip. 24 hours later I lost all sense of balance, became hot and clammy, nauseous etc. It passed within a few hours. After flying home a few days later I noticed that when standing in the kitchen I could feel the floor moving up and down (logically it wasn't, I figured I had sea legs). Ever since then I have been intolerant to motion of varying degrees. But the odd thing is it doesn't make me sick, it makes me dizzy. Not a spinning dizzy, but an up and down swaying dizzy.
The worst is when flying. On take off and landing I feel an incredible heavy crushing feeling in my head and I have to fight with everything I have to not lose consciousness. This feeling also happens when the plane 'dips' during the flight. I get so anxious about this feeling that I avoid flying. I feel the movement of a pontoon over water as far more exaggerated than it is is, I struggle
to stand up. I hate going in elevators as I can feel the movement even before I get on and still after I get off. Sometimes I have to hang on to the mattress when my husband rolls over in bed at night because I feel like I might fall off! I can't go on a trampoline or jumping castle with my kids and if I'm on an escalator I have to walk on it to lessen the feeling of the movement.
As an aside, may be related, when I feel dizzy and therefore anxious/panicky, my way of 'coping' is to cause pain to myself. I pinch, scratch, bite, pull my hair etc, anything to feel some sort of external stimulation to distract me from the internal horrible feelings. The odd thing is I often can't feel the pain until later, and will therefore be covered in bruises without realising it.
I am seeing a psychologist for the anxiety, but he doesn't seem to get that if the motion issues went away so would the anxiety, I am sure of it. I have seen 2 ENT's about the motion issues but they don't have ny idea why I feel it except that as soon as they hear I have anxiety they write it off as 'all in my head'.
So I guess I'm wondering if it could be a sensory issue? Does anyone else understand where I'm coming from? Can anyone relate to this?