Sounds like meditation techniques. I often practice mindfulness meditation in a dark room for ~10 minutes in the mid-afternoon when I get tired. It usually gives me new energy and focus similar to if I'd napped.
In particular, the part in the OP where you "picture yourself being on lake, etc" looks to me as completely anti-meditation.
The trick is that I do it laying down instead of a more conventional meditation position.
see http://marc.ucla.edu/mindful-meditations "Body Scan for Sleep" for example