As the fitness benefits of proper sleep pile up, more trainers are advising their clients to get more Z’s. But that’s not always such a good idea.

When a client freaks out over three pounds she gained overnight, or celebrates five pounds she lost for no obvious reason, use this handy guide to help make sense of it.

From “how much?” and “how often?” to supplements and vegan options, here are the answers to your clients’ most pressing questions.