Ones I’ve seen and enjoyed –

Dark City
The Matrix
The Prestige
Total Recall
Existenz
Abre Los Ojos / Vanilla Sky
Alice in Wonderland (Anything except Disney versions)
Memento
Inception
Orlando

Ones that other people have recommended for this category but I’ve not seen yet or don’t remember well enough –

Cube
The 13th Floor
Videodrome
Jacob’s Ladder
12 Monkeys
Sphere
Minority Report
The City of Lost Children
Hitchcock – Spellbound
Equilibrium
Kurosawa – Rashômon

So, if you want to inspire a sense of alternate reality without doing drugs, watch a few of these back to back.