When I looked at the Wikipedia page on Elisa Lam, it showed a list of four medications she was taking for her bipolar disorder.
These have the following side effects that most likely led to her 'accidentally' committing suicide by drowning herself in the water tank: 1. Effexor: out of control actions, suicidal thoughts, uncontrolled excitability. 2. Wellbutrin: confusion, restlessness, delusions, hallucinations, mental disorder with loss of normal personality and reality, suicidal ideation, panic disorder. 3. Seroquel: confusion, uncontrolled movements, agitation, anxiety, delirium, psychosis, paranoia, delusions, suicidal ideation. 4. Lamictal: anxiety, confusion, depression, jerky movements, hallucinations, delirium.
(Side effects gotten from WebMD and Drugs.com).
With all of this going on in the poor girl's head, it's no wonder she acted strangely. My only question is how did she get into the water tank? It was 8 feet tall, and had a heavy lid that would have been difficult to replace after getting inside. She somehow pulled herself up onto the tall tank, opened the lid, took off her clothes, then climbed inside.
I think she was probably going to jump off of the building at first after climbing up the fire escape (the only unlocked way she could get to the roof without setting off the door alarms). She then decided she couldn't do it, and somehow climbed up on the water tank, subsequently drowning after she got inside. She was obviously not her normal self, as the video shows. Condolences to her family.