There's a really good pamphlet available online called "what is dissociation" put out by a group called Caritas (just google both) that does a good systematic and simple job of explaining it. I actually used the pamphlet to explain my symptoms to a few friends. This is a symptom I have WAY too much experience with! But, fortunately, much less as time goes on.
kers description is quite accurate. It can feel like floating away, detaching, or more extreme - flicking the switch and no longer being present (and sometimes later "losing that time" and not knowing what happened). For me in the extreme I can't talk, or move. In more subtle versions, I'll start feeling distanced, I may be able to talk but it will be slower, more deliberate and harder for me. I may be easily confused or disoriented or have trouble making decisions (like whether to cross a street - very simple ones). I often stare at the ground when this is happening or have trouble making eye contact.
I've found grounding techniques help (feeling different parts of my body and identifying sensations), changing my physical stance if I can (ie stand up, sit down), turning on lights, taking off a sweater so I'm cold (or vice versa), drinking water, or tasting something strong. It's important to be kind to yourself (this took me a long time to learn). Now I treat myself as a kind parent would - and try to talk myself through it - it feels like you're going away, did something upset you? was it maybe when X said X? Did that remind you of something? It's okay to find that upsetting. But you're somewhere safe right now. Let's take a few moments and come back.
In the more extreme, I'd need to take meds and then sleep. Dissociating does really tire me out (the more severe form, which I don't get anymore would potentially have me in bed for several days). I also used to dissociate in therapy every single time. My shrink was very patient, and we spent a lot of time exploring what it felt like physically. It also used to affect my sight, hearing and sense of temperature.As I'd go in and out lights would get brighter or dimmer, background sounds (like a fan) louder and soften, all of a sudden I'd be very cold.
Also just to note dissociation is on a spectrum- with daydreaming on the mild end. Spacing out for a few moments when tired, or thinking about something else is normal, it's linked, but at the normal end of the spectrum. I had one therapist who always asked me where I went, but I never had any idea and that wasn't a productive strategy. I was just "gone" - the approach my shrink used was, to me, more helpful as I wasn't retreating anywhere in particular, I was just spooked my something and then gone.
Finally, it is really important to get treated for this. My first attempt didn't work out (the guy kept trying to get me to say what I was thinking, but I couldn't talk, and wasn't thinking anything I could identify), and I actually got worse - I started dissociating in more and more and more situations. This starts to get dangerous, and your brain starts to use it as a short cut to avoid everything. All of a sudden even things that were very midly stressful would cause me to dissociate, and I was dissociating every day, several times a day. Actually getting better, means dissociating less, and less profoundly and having fewer triggers, and trying to wean your brain off of this "escape mechanism." Of course, this means feeling things you might not want to, which can be awful, but in my experience - way way better than feeling absent half the time.
I'm not sure if this will help - it sounds like you have fleeting, relatively light dissociation. But it might be just something to keep your eye on. Be gentle with yourself, but try to pull yourself back if you can (or ask for help with teachniques to do this) and maybe there's a friend you know well who you could ask to tell you when they see this happening, so you can get a sense of how frequent it is.
Take care, and best of luck.
