I couldn't find any topics regarding this phenomenon so I thought I would make one myself, to help other users that are freaking out after an experience like this.
http://en.wikipedia.org/wiki/Hypnagogia
First of all - Hypnagogia is transitional state between wakefulness and sleep (i.e. the onset of sleep). Hypnagogic hallucinations are the result of being stuck (for a very short period of time) in this state (between sleep and wakefulness). To put it in simpler terms, you are awake but you continue to see part of your dreams.
I had one experience in my life. Upon waking up a couple of years ago (during a rough anxiety period), I saw a bunch of spiders creeping up a wall for a couple of seconds, wich made me jump out of bed and have a panic attack, followed by a quick visit to the mental institution, where I was laughed at . The doctors, after listening to my story and laughing at me cuz I thought I was schizophrenic, explained that this is a common ocurrance and every single person will experience something like this, being stuck in between a dream state and an awake one at least once in their life time, but that anxiety sufferers can get them much more often, because adrenaline "squirts" sometimes make them awake very fast.
Upon researching when I got home I found a lot of stories, most of them funny (after you know what caused them), and now, thinking about making this thread I had to google the symptoms again because I couldn't remember what it was called (hypnagogic - not your normal scrabble word) wich made me laugh even more: people awaking to see huge giraffes biting their toes, monkeys swinging from their lamps, old ladies killing themselves (ok this one is not funny but it's cool) etc.
If any of you have stories like this, feel free to share them.
P.S.: Users that have experience with Sertraline or other ADs might have had as a temporary side effect vivid dreams and things like that, wich are quite similar to what I have described.
-IF the thread is in the wrong section I kindly ask the admins to move them to the correct one-