Thanks for your answers
@Robot_Butler: yeah, I knew I was dreaming although my reality checks wouldn't work. But as I assumed it was not my dream (I still don't know why I came to that conclusion) I couldn't control it, except for the moment when I imagined my girlfriend sinking into the ground and it really happened, I'm not sure if that can be seen as some kind of control. And usually I have the same experience as you do, my dream characters and even my own mind try to convince me I'm in waking life or at least they try to distract me from asking myself whether I'm dreaming or not but this time it was the opposite lol.

@ShadowOfSelf Now, remembering the dream, I know that she was only a DC as you said^^ But as you already mentioned my logic wasn't quite that accurate during the dream, even though I knew everything that was happening was just a dream. But for some reason, my mind told me it was her lucid dream (maybe because she was the one telling me it was a dream and doing things that made me aware of the strange things happening around me) and I was some kind of guest and maybe that's the reason why I didn't get 100% lucid. Thanks for the advice of using another reality check, I'll try to get into the habit of doing another one. I hope it won't be too difficult, as the reading or watching a phone screen or digital alarm screen happens spontaneously in my dreams, even before I want to test if I'm dreaming. That's the reason why I often use that kind of reality checks, because they usually work as dream signs for me and I just have to repeat them intentionally just to be sure.

So, anyway, thanks to everybody. I will try some other reality checks next time I am not sure if I'm dreaming.