What is a vision (ru'ya) and what are its types in wakefulness and sleep? And how do we distinguish it from a dream (hulm)? And is there a connection between a person sleeping on their right or left side and that?

The term "ru'yah" (vision) is used to describe a person's perception of something and their knowledge of it. As for what occurs in a dream, the common term used is "ru'ya" (dream). Scholars have designated "ru'ya" for the good, gladdening visions a Muslim sees, and "hulm" (nightmare) for the devil's manipulation of a person, wanting to cause them distress. This is supported by the hadith: "The ru'ya (good dream) is from Allah, and the hulm (nightmare) is from Satan." We do not know of anything that indicates sleeping on the right or left side has an effect on this matter, except that it is from the Sunnah to sleep on the right side. Following the Sunnah is a cause for success in this world and the hereafter, and for improving a servant's condition in both.