I've had two lucid dreams in the last 7 weeks or so, and they've been the first two since I was a child (I used to get them naturally on rare occasions but didn't really think twice about them).

My first lucid came to me as quite a surprise. I had horrible dream recall at the time and definitely did not expect to have a lucid. I was not ready for it and ad a result lost it quite quickly. I would say it only lasted for about 5 seconds.

My second lucid happened about 2 nights ago. I was running in a field of green grass when all the sudden I realized I was dreaming. It was an intense feeling at first and I could feel my lucidity going out the window. Sadly, I lost that one too within about 10 seconds.

Something weird about both occasions is I do not even recall what triggered the lucids. I can't remember why I realized I was dreaming. I didn't do a reality check, I don't remember anything unorthodox happening, etc, etc. The only part of my dream I remembered was the 10 seconds of knowing I was dreaming.

Is it common to not know what triggered the lucid?