I can tell you what's been related to me about ambien. Many people I know took it for a year (some less) it worked great and then just stopped working completely.

I don't know if this is what you were saying but it seems very common for ambien to suddenly stop working.

I don't know about Sonata, sorry.

I would also like to know if any other sedative/hypnotics are available through OPs, great question!

Steve