Eszopiclone, also known as Lunesta, is a nonbenzodiazepine "Z-Drug"(the same category as zolpidem(ambien)) that acts as a depressant due to its actions at the GABA subtype A receptor. Basically, its a depressant that shares some qualities in common with benzodiazepines. The primary difference, at least from what I've read, is that drugs like Eszopiclone and Zolpidem, while being sedating, are less euphoric that benzodiazepines. There is always a risk when mixing CNS depressants, in your case tramadol and eszopiclone, but with this combination the risk should not be as high as with benzodiazepines. However, this is not to say that this combo is competently safe, and to avoid the risk of complications like death you should dose both drugs at 50%-65% of your usual dosage, and slowly work your way up, stopping if you find that your breathing is getting too shallow.