I'm not on meds, so I don't know if your meds could be causing these problems. I can tell you, however, that I obsess about everything, and that includes existential questions. It's really because I think too much. I can't stop my thoughts. And I question *everything*. I'm an overanalyzer.
Is there a chance your sudden existential questioning could be related to the common "control" issues of anxiety? That's really where mine lies. I can't stand the thought of the unknown...not knowing what will happen to me for sure when I die. People who have anxiety often have issues of needing everything to be in control around them, and needing to feel in control. A lot of anxiety stems from the inability to control something (personal health, relationships, thoughts, etc.), which in turn eventually leads to the question of "ok, if something horrible does happen and I die...what's after that, if anything"? Therein lies the existential questions that we then begin to obsess over.
Do you also have a fear of heights, by any chance? I ask because I do, and I also often have the same spacial thing you have. I get dizzy looking at the sky sometimes, but mainly, I can't look at pictures of outerspace without feeling a dizzy, disconnected, "gotta run away from it before I fall and get lost in oblivion" kind of feeling, if that makes any sense. I have a pretty big fear of heights, too. For example, after 9/11 and seeing people jumping/falling from the buildings, I will periodically get a flash of one of the towers in my head and then I have this terrible sense of falling. It's hard to explain, but I know it's connected to my anxiety.
I suffer from depression in addition to Generalized Anxiety, by the way.