Is it possible for one to pray and be afflicted with Riya' (showing off) without realizing it? If so, how can one combat this type of Riya'? Does it invalidate the act of worship? And is feeling embarrassed during prayer considered Riya'?

Riya' (showing off) is a disease of the heart that nullifies deeds or diminishes their reward. It is a minor form of Shirk (associating partners with Allah). A Muslim must strive against their self to avoid it and maintain sincerity in their worship. There may be a hidden form of riya' that a person does not perceive, and to treat it, the Prophet, peace and blessings be upon him, guided us to the supplication: "O Allah, I seek refuge in You from associating anything with You knowingly, and I seek Your forgiveness for what I do not know." The deed is invalidated if riya' is the sole motive for it, and the reward is diminished according to its degree. Hidden riya', which its owner is often unaware of, usually does not nullify the deed, but one must accuse oneself of it. If a worshipper finds a difference in their worship when being observed versus when not being observed, this indicates the presence of an element of riya'. However, not all riya' nullifies the reward or corrupts the deed; rather, there is a detailed explanation for it.