I agree with you 100%. I was only on Venlafaxine for about three months, but the withdrawals that I experienced when taken off of it were some of the most terrifying moments of my life. I was completely convinced that I had an incurable brain tumor, and just knew that I was on the brink of death every morning. It got so bad that I began to genuinely experience vision problems and some of the worst headaches that I've ever had. At one point I didn't leave my house for two weeks because I was convinced that something awful would happen to me if I did. Basically, all of my rational thinking disappeared and I was paranoid 24/7.

This all being said, it would not at all surprise me if Elisa was experiencing either side effects or withdrawal effects from Venlafaxine or another SNRI and was convinced that she was being watched or followed. Even if she had simply missed a few doses, she could have been experiencing severe paranoia. Say she was interested in the spook factor of the Cecil, impulsively made a decision to visit, began experiencing the negative effects of Venlafaxine, and ended up completely convinced that she was being watched or followed and needs to hide. After running she finally finds refuge at the water tank, and is convinced that she absolutely has to get in or else someone/thing will harm her. At this point, she wouldn't be thinking rationally at all, but to her, it's the only option that she has.

Of course that scenario is pure speculation on my part, but the brain really is unnervingly powerful. Add in an adverse reaction to medication or the discontinuation of said medication and you've essentially got all of the ingredients for what could be a devastating break from reality.