The most commonly reported
side effects are sleepiness or excessive sleeping, dizziness, dry mouth and weight gain. Other side effects include akathisia (an inability to sit still), constipation, dizziness, orthostatic hypotension and tremors.
The yawning you experience is also a rare side effect reported with Zyprexa.
(Ref: http://bipolar.about.com/cs/zyprexa/a/meds_zyprexa.