Don't know whether this helps, but in Win Wenger's "Einstein Factor" he says that Image Streaming without describing verbal images aloud results in sleep. That's why you should always do it aloud with a tape recorder or person to document what you say. He's right! If you're comfortable enough, when the images start to come and you let them flow, you'll go out like a light!
I tried some off-prescription sleeping pills a few years ago when I'd been working nights for months and couldn't get back into a normal pattern of being awake during the day. They didn't really work, and just made me feel as though I had a hang-over. Drinking will make you sleep too, especially if you are not used to it but I'm guessing you don't want the side effects of waking up feeling off-form in the morning!
I should try Image Streaming next time I have a long-haul flight. I can never sleep on planes, although I would sometimes dearly love to. How do you get to sleep on planes? I think you have to be comfortable to sleep with Image Streaming so I guess that won't work so well.