A tail held high usually means a high emotional state of arousal or excitement, but that on its own does not tell you whether an animal is in a positive or negative emotional state.
High arousal can be appetitive, meaning the animal is interested and anticipating something good, or the emotional state can be in threat and protect, so the animal is expecting confrontation.
A lifted tail generally means mild arousal of interest or anxiety (threat and protect). The emotions are not strong and can easily go one way or the other. This is often an in-between stage when the animal is assessing a situation.
(Issue 48, May 2021, pp.48-51). Read article