Have you ever had a seizure? Do you have any relatives with epilepsy? Sometimes very minor seizures can cause people to feel detached/dissociated. Remember that most seizures don't cause people to convolse on the ground like the grand mals tend to. Sometimes people will stare off into space for a few seconds and most don't realize what just happened. It's possible to have a seizure while maintaining consciousness, these are called simple partial seizures.
Here's a short clip which shows what it can be like
http://www.youtube.com/watch?v=gwIoCm0Ict8
There are a couple types of partial seizures which can cause experiences of detachment
~Sensory Parial Seizures- These cause your senses to become a bit distorted for a time, things mights sound louder or you might feel like things are changing sizes. Sometimes things may seem closer or farther. A lot of people also
~Psychic Partial Seizures-These are type that usually cause dissociation, derealization, and depersonalization. You might feel like you are not you for a bit or that you are like an outside observer. It can also just be a feeling of disconnection. Some people will have out-of-body experiences during these.
Psychic Partial Seizures can also cause you to feel very strong emotions for a period of time usually fear or anger as these tend to affect the amygdala. A lot of people also report deja vu type experiences during these, a strangness of though, or a bit of loss of time. Hallucionations are common.
~Motor Partial Seizures- These can cause slight movements similiar to tics such as shaking legs, twitching, blinking and so on
It's not uncommon for someone who's have a simple partial seizure to experience more than one catagory at once. If any of this sounds like something you think you might be experienceing it would definitly be worth your while to see a neurologist. EEGs can detect seizures almost 95% of the time and there are a lot of very effective medicines for epilepsy.
I don't have epilepsy however I've had two simple seizures because of insomnia (I had gone about 5 to 7 days without sleep each time, sleep deprivation is a MAJOR trigger for seizures)
The first time was really strange I just suddenly had this intense feeling of fear, I couldn't move but I wanted to run. Then I just heard this voice saying "I am God, Do Not Be Afraid" I still couldn't move for a couple more seconds then all of a sudden I just realized a few seconds had gone by (I had a stare out).
The second time it began as a simple seizure when I suddly couldn't move again, felt this intense fear, and then heard all these voices I couldn't make out. From there I began hearing this extreamly loud horn like beep which eventually drounded out the voices. The the seizure generalized meaning it was no longer simple as it was affecting more than one part of the brain and i lost consciousness.
Most experiences of dissociation/detachment/derealization aren't epilepsy or seizure related, however it's always good to know that they can be. I know that it can be really scary to not know what's going on. I think I had just lost my mind for a long time. It's really great that you're able to post and looking for more information. You seem like an extreamly insightful intelligent person.
~Jen