Lucidity is exhausting!

I had two very short LDs recently and I'm hoping I'll get the opportunity to have more. However the last two times I found the effort of staying lucid and holding the dream together just too exhausting. It probably didn't help that was trying to manipulate the dream and it wasn't working (much to my disgust - I'm supposed to be good at this!). Both dreams were quite old and probably nearing their end, so it may have been a losing battle to begin with. In both cases I had to give up and wake up.

I've experienced this before, back when I was eight and the phrase "lucid dreaming" would have just resulted in a blank look. In some dreams this feeling of exhaustion used to be present even when I wasn't actively trying to change things. I never really fixed the problem either.

Anyway, my questions are: Am I trying too hard, or am I too lucid and have unwittingly started to wake myself up? Does anyone else have similar experiences? How should I react if I manage to get lucid again?

I get exhausted in LD's every once in a while, but mostly it's just a paranoia thing. When I'm afraid that the dreams ending I start to get really worn down and I can't perform well in the LD, then the dream fades. When I'm feeling particularly confident I don't seem to have the problem at all.
Next time you're lucid, just don't worry about it. It might be the end of the dream, but the exhaustion is probably all in your head.