What are somnus?

Some articles on somnus:

Hypnos
... Greek Ὕπνος, "sleep") was the personification of sleep the Roman equivalent was known as Somnus ... word "insomnia" comes from the name of his Latin counterpart, Somnus ... (in- "not" + somnus "sleep"), as well as a few less-common words such as "somnolent", meaning sleepy or tending to cause sleep ...
Semele (Handel) - Synopsis - Act 3
... Somnus is sleeping peacefully in his cave when Juno and Iris arrive ... It is only when Juno speaks the name of the nymph Pasithea that Somnus awakes ... In exchange for the nymph, Somnus agrees to help Juno ...