Hi,
Although episodes of mania often affect sleeping patterns and the two are connected this realtionship is complex and indirect. Sleep alone did not cure your mania, its the antipsychotic/antimanic effect of the Zyprexa that cured your mania, the sleep was just a (beneficial) side effect.
During my first (unidagnosed) manic episode, I went to my GP and got sleeping pills, for what at the time I told her was insomnia. The sleeping pills did nothing to cure the mania. They would knock me out at night and I would wake up in the morning still manic. This is because the mechanism by which sleeping pills/sedatives/tranquilisers work is totally different from medications known to be able to treat mania.
To get technical, Mania is a very complicated and misunderstood process. From postmortem studies of brains, it has been postulated that there is a dysfunctional protein in the brains of bipolar people, which for some unknown reason suddenly increases at certain intervals and this causes the monoamine system (dopamine, norepinephrenine, seratonin) to go haywire and become extremely hypersensitive. Atypical antipsychotics (e.g. Zyprexa) directly on the monoamine system; by antagonism/partial agonism of Dopamine D-2 receptor and antagonism/partial agonism of certain seratonin 5-HT receptors; in order to bring things back into balance. Lithium has a dual effect, it downregulates the monoamines, by slowing release of Dopamine and Norepinephrine, and, in the maintainance phase, it blocks the dysfuctional protein from triggering manic episodes in the first place. Lithium and most modern atypical antipsychotics have similar rates of success in treating mania, with antipsychotics having a slight edge because they work quicly wheras Lithium takes a few weeks. However, for long term stabilisation Lithium is preferred due to this dual effect. Sedatives such as Valium, Xanax, Ambien worked totally differently. Valium acts by opening up GABA channels, which are responsible for the sedation of your entire central nervous system. However, this effect is temporary and is not the direct mechanism for mania. So, after you wake up you will still be manic.
Sorry for the science lesson, but you asked so there. Bottom line is, sedatives and drugs known to treat mania work in wildly different ways. Valium is occasionally given short term to people with mania to take the edge off if they are feeling extremely anxious, however, using Valium alone to treat mania would be totally ineffective. There is a relationship between mania and sleep, but this relationship is indirect and you can't simply sleep off mania. It doesn't work like that. We are only now starting to understand the mechanisms of mania. The drugs used today were developed before they had any credible theories to explain mania, by trial and error. Lithium by a doctor who tested it on hyperactive rats and found that it sort of calmed them down and antipsychotics because they were known to work on people with Schizophrenia and so they wanted to try it on people with bipolar. No one knows why some antiepileptic drugs such as Valproate/Lamotrigine work, but people who had both epilepsy and bipolar found that these drugs had an effect on reducing not only seizures, but also treating their bipolar.
Hope this answers your question.