the first floor is where the wards for creature-induced injuries is located. if you ever get bitten, stung, burnt, or any other magical creature-related injury, here is where you will go.

the second floor of the hospital addresses anything bug or disease related. magical, of course. Some diseases are common, like a Muggle chicken pox or head cold. Sometimes they're serious, like contagious magical maladies such as dragon pox, vanishing Sickness, and scrofungulus. and then there are some that are unknown and life threatening...

the third floor deals with potions that have backfired, either physically, internally or mentally, and plant poisoning. all sorts of cases come here, from uncontrollable giggling to rashes, regurgitation to hallucinations, and any other unwanted outcome from plants and potions. Every so often these cases turn into a case for the magical bugs and disease level if the backfired potion goes very... wrong...

the fourth level of st. mungo's is pretty explanatory. Anything to do with backfiring spells or charms, effects of curses, unforgivable or not, and any unliftable hexes or jinxes are found on this level. depending on the circumstance, this is where those who were tortured the worse in the Second wizarding war reside.