The difference between day dreaming, thought and dreaming at night

Hey,

Like the title says, i have a question about the difference between day dreaming, deep thought and (real) dreaming.

So can anyone tell me how you can be sure that you were dreaming and not just thinking. Sometimes when i go to bed and i try to sleep after a while (when i'm sure i'm awake) i can not tell if i have just been thinking all the time or if i fell asleep, dreamt and woke up again. This may sound stupid to some people but for me some of my thoughts, while trying to sleep really look like dreams.

For example last night i saw my fingers grow longer. And i thought to myself 'wow, this can't be' (because this would be my first lucid dream) and like 2 seconds later i realized that i was trying to sleep in my bed. But i can honestly not tell if i was thinking the hand thing or if i was dreaming it.
So where lies the border between dreaming and thinking (half asleep)?

Dreaming - Imagining something when you are asleep
Thinking - Imagining something when you are concious and awake
Lucid dreaming - Dreaming and concious thinking combined

I think what you're experiencing is the border between waking and sleeping, known as hypnagogia. This is where you are not quite asleep but you're mind is drifting and your body is falling into sleep paralysis. You may be experiencing tiny dreamlets which last no more than a couple of seconds, or hypnagogic imagery. Not quite a dream but almost :)