Im going bananas

Im going bananas is a term used when you feel like you are going crazy or insane. Bananas have long since been used as a symbolism for acting weird, strange, crazy or insane in the mentally unstable sort of way which is why they are used as the example in this phrase. By saying you are going bananas you are acknowledging that things are starting to happen around you and causing you to act quite different than how you normally would.