If you change your conscious perception of space and time, it will both change in real-life and the dreaming world, which would screw you totally.
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I wouldn't be surprised if there were some substances that you could abuse for that purpose. I was prescribed codeine for my wisdom teeth extraction, of which I saved some. It gave me the opposite effect, I did not fall asleep, but those were the fastest 4 hours of my life. Mildly fun, but not something I would repeat.