Allergies can cause sleepiness, for example if I eat something that my body does not like it will send me to sleep quite quickly, I think the key is to try to discover what is the cause, I have found it helps to keep a food diary.
Samantha, 45 yrs
Stopped smoking Jan 2013. Diagnosed Left sided UC, 8th Feb 2014.
Pentasa 3.5g daily, Vit D, Multivitamin, Vit B12, 500mcg Molybdenum
Gluten, Dairy and Sulfite free.