I have always learnt that 'to get out of bed' is 起床, but a book of mine says that two elderly people 从来不下床. Is there a difference between the two or is it just a dialect thing? Also, if you can say 下床, can you say 我上床 to mean 'I am going to bed'?
Alright, to me, 起床 means the end of sleep and getting up. 下床 means the opposite of being on the bed, as in your example, two elderly people 从来不下床 may mean that they have health problems so they have to be lying on the bed, but they may not be asleep when they are on the bed.
上床 can be used to refer to the action of going to bed, like 我一般晚上 11 点钟上床。(I usually go to bed at 11 pm.) Also 上床 is the common saying of having sex.
上床 generally means that you have moved to bed, but not necessarily to sleep. You can read books and other activities in bed. For example: 我上床去睡觉。 下床 is you leave the bed, first, there is a temporary departure and will come back within a short time; second, the location of the move, for example, you just read in bed, and now get out of bed to the sofa to read a book. For example: 我下床穿衣服。 And 起床 often is used to represent a series of actions that awaken from sleep. The coherent behavior of sleeping from bed, sleeping and opening your eyes, sitting up, getting out of bed, and washing yourselves can all be called up. For example: 我起床去工作了。