1. To become somewhat eccentric, odd, or mentally unbalanced. Jackson started going dotty after spending a month by himself in his cabin.

2. To become forgetful or absent-minded, especially due to senility or old age in general. Grandpa's been going a bit dotty lately, I don't know if he can take care of himself anymore.

3. To become very excited or enthusiastic (about something). I've never understood that pop star's popularity, but kids just go dotty over her music.