The SP trouble is very common in East Asia, where the main food is rice. It has been supposed that it was due to glutamate (which can be found in rice) but nothing really proved it until now.
I’ve recently read an interesting scientific report, where it was shown that glutamate receptors play an important role in the regulation of REM sleep. Hence it could be related with the observation above.
So if you wan’t to experiment the SP trouble, you can perhaps eat a lot of rice.