In Catholicism, you have to confess all mortal sins, specifying number and any circumstances that may increase or decrease the seriousness of the mortal sins (as the priest judges the penitent in Catholic theology). I find this kind of confessing very stressful.
Is this how it works in Orthodoxy?
In short, no.
Having said that, one must note that there are a variety of Orthodox confessional practices and styles that are as diverse as the individuals involved. Why? Because, above all else, confession in Orthodox praxis is relational
. Ideally, one would confess to a given priest for years at a time, thereby developing a relationship founded upon prayer, honesty and sacramental grace. Some spiritual fathers may require more detail; others may want to talk about trends and specific problems, based on long knowledge of the person's strengths and weaknesses. The ultimate purpose of the confessional is not juridical, but therapeutic -- although there are some who tend to bring it more toward the former, e.g. by insisting that all unconfessed sins will be held against one's soul by demons in the Tollhouses (but that's ANOTHER story!!).
Anyway, St. John Chrysostom says that one should confess one's sins to God every night. Having done so, one can then begin to identify patterns and passions from daily self-examination. These patterns and passions, he says, are the stuff that one should discuss with one's spiritual father in confession.
On the other hand, some Orthodox sources, especially those coming out of the more Latinizing eras in Russia and the Ukraine speak in detail about mortal and venial sins, but, in general, such are not especially developed categories in Orthodox ascetic literature. Nevertheless, it seems to make good common sense to readily confess any major sin, no?