One of the themes in the academic study of the prophets is ecstatic behavior of prophetic figures. Prophets fell into trances, convulsed, and participated in otherwise strange conduct. The idea stems in large part from ancient Near Eastern parallels that refer to such figures with vocabulary similar or identical to that found in the Old Testament.
The notion might sound odd, but there is biblical precedent for it. For example, prior to becoming Israel’s first king, an episode in Saul’s life gives us some insight:
When [Saul] turned his back to leave Samuel, God gave him another heart. And all these signs came to pass that day. When they came to Gibeah, behold, a group of prophets met him, and the Spirit of God rushed upon him, and he prophesied among them. And when all who knew him previously saw how he prophesied with the prophets, the people said to one another, “What has come over the son of Kish? Is Saul also among the prophets?”
Elsewhere in the Old Testament, the coming of the Spirit on a person enabled superhuman strength (Samson; Judg. 14:6, 19), special wisdom (Isa. 11:2), and visions (Ezek. 37). It was often associated with divine enablement for a specific task, like kingship (1 Sam. 16:13–14) and judgeship (Judg. 3:10; 6:34). The notion of ecstatic behavior, however, more clearly comes from the odd behavior of certain prophets.
Ezekiel is likely the most familiar example of strange prophetic conduct. God told Ezekiel to do several strange things. Ezekiel was told to draw a picture of the city of Jerusalem on a brick tablet and then smash it as a visual aid of how the city would be under siege (Ezek. 4:1–3). God commanded him to lie on his side for 390 days, and then forty more on his right side to symbolically commemorate Judah’s punishment in exile (Ezek. 4:4–8). He shaved his head with a sword, then after dividing the hair into three piles, burnt a third, hacked another third with the sword, and scattered the rest into the wind—more performance art about what would happen to Judah and its population (Ezek. 5:1–12). On yet another occasion God told him to publicly dig through a wall and escape through it with the baggage of an exile (Ezek. 12:1–12). If the themes of his behavior hadn’t been so disturbing, he’d have been a source of regular entertainment.
Ezekiel isn’t the norm, though. Prophecy was mostly about preaching, not unusual abilities to predict the future or performing bizarre and symbolic acts. Some prophets did such things; some did not. In any regard, they were not mentally unbalanced. Whatever God told them to do, or when the Spirit came upon them, there was a point to it. God had a message, and that message needed to be taken seriously.