Nan-next-door and the lettuce sandwich

When I lived with Nan-next-door my regular pre-bed supper would be two slices of white bread, spread with butter and filled with a generous helping of lettuce.  Nothing more - no cheese, ham or sandwich spread (very odd stuff  sandwich spread - why would anyone want to eat something that looks and tastes like vomit?)   I imagined that the lettuce sandwich was standard gourmet fare for the children of Oxfordshire and we were all tucking in at aabout 7.30.
Recently when awake at 4.00am (insomnia, not hectic social life - I regret to inform you) I was desperately searching cures for sleeplessness on the Internet.  I found the usual suggestions: warm baths, massage, drink milk etc.  But the more esoteric ideas caught my eye: put a small weight on your body (how small 500g, 1kg - any bigger and that sleep might be permanent) or take extract of sea snail entrails (this being Japanese I began to muse on what the South London equivalent would be - suggestions gratefully received).  Others also wouldn't do: I can't curl my toes otherwise I get cramp and really don't fancy rubbing my feet with dormouse fat and where do you get dormice from?  Although I suppose I could have substituted the hamster when it expired.  See the following for more detail:
http://www.mentalfloss.com/blogs/archives/24139

I also found a reference to eating lettuce to help with insomnia - supposedly they contain natural opiates which act as muscle relaxants.  Perhaps this is some ancient folk cure passed down from mother to daughter since time immemorial and Nan-next-door wasn't just being a cheapskate.