How much would you typically see a bp drop while someone is sleeping? is there such a thing as too low when you can't tell if they are havin symptoms?

No rule of thumb: The lowest bps are often recorded at the time of or during sleep. BP doesn't usually become too low though because people are lying down during sleep and can perfuse their vital tissues more easily. Moreover, because they're resting, their needs are less. If BP is not too low during waking hours, it won't be too low at night, even though it's lower.