What made Rivkah partially slide off the camel when she saw Yitzchak?
Rashi: She was awestricken by Yitzchak's awesome appearance. 1
Seforno: She inclined her head out of respect for Yitzchak.
Rashbam: She was riding like a man (each leg on a different side, out of fear, due to the height of the camel), not side-saddle, like a woman, so she moved to a more modest position.
Ramban (citing the Ibn Ezra): The Pesukim are inverted, and she slid off the camel after Eliezer, in reply to her query (in the following Pasuk) told her who 'the man' was.
Ramban: She sensed that the man coming towards them was coming to greet them or to invite them to come and stay with him, so she acted modestly in the way of women, and she turned away from him.
Ha'Emek Davar: He appeared like an angel; his hands were stretched in prayer. According to the Ramban's version of Rashi, she descended out of embarrassment).