I've actually had this problem for about 5 plus years but not sure if it's the same thing. But I get itchy skin when hot or do anything that increases blood flow/ heart rate. This can include have a hot shower, small physical activity like walking or even when I'm asleep and I'm having a dream with a bit of action. This one often disturbs my sleep but the good thing is, it doesn't always happen when I sleep. I've spoken to doctors, they don't seem to know what's going on really. I do live a majorly sendintery lifestyle tho which I think can be a contributing factor, but also because of this, I've have blood test and doctors have found that I'm also diabetic with very high blood sugar levels, we're talking blood glucose levels of 18 when normally it's between 4 to 6 so even this can be a contributing factor. My itching usually happens on the back side of my neck, all over my back as well and all over my head mainly, but can happen around my belly and chest too. The thing is after I've been out for the day, the itching actually stops and I'm fine for the rest of the day. It's just that initial 20 to 30 minutes of itchiness that can be quite uncomfortable for the most part. I have a few raised bumps on the outer part of my thighs and legs but just a very small amount on the back of my right arm and this can feel rough when sliding my fingers across.