In my case dissociation and derealisation go hand in hand.
I used to complain to people that starring at a computer monitor all day made me feel dizzy and light headed. The reality is that I suffer from a derealisation disorder. I thought it was perfectly normal to feel that the wole world had changed visually by lunch time every day.
My solution, buy expensive monitors to reduce this effect. It never worked but it worked as my meaning.
What does it feel like?
Lights seem brighter, familiar things seem strange, the world looks more vibrant but not really in a good way.
Simple walking feels strange and I find that my body has armoured up, by that I mean tensed up to such a degree that I have to grimace to make my face feel normal again.
What causes it
Derealisation disorder has been explained to me as a sort of attention deficit.
By that I mean if the brain has the capacity for 100% attention, mine uses 70% to look outwards and spends 30% looking inwards. It is a bit like looking at a pixelated image, I simply do not have enough RAM to see thinks correctly. My brain is overloaded. The result I feel detached and surreal.
There are many causes trauma being one of them.
Knock yourself out here Feeling ‘Unreal’ http://www.anxietycare.org.uk/docs/unreal.asp