http://www.uesp.net/wiki/Skyrim:Sleeping_Tree_Sap are your friend.

...it really amazes me when people on a forum - a place where it's designed to be a COMMUNITY built through communication - just results in uploading links or, worse, tell you to google search it.
Ahem...
To PROPERLY answer your question OP:
Spoiler The Sleeping Tree Sap is sap from a unique tree found in Skyrim... there are several tales about it, many of which Ysolda in Whiterun can tell you about it. So... it's not "suddenly" a new form of Skooma... it's a new specific sap found in Skyrim itself.