Sometimes i have sudden urges to do things like fly across the country for no reason or impulsively buy a tarantula even though i know i will regret it the next day. then i just have to do it. does this sound like a mental illness?

Compulsive behaviors like those you describe are often a stress management response to issues you are either not aware of or choose to suppress. I would look for a life coach who could teach you productive/effective stress management skills. During the process you may uncover and be ready to explore deep stressors more effectively. Somewhat mental, but not crazy mental. Do the work.

Obsessive compulsive disorder comes to mind. It is imperative that you see help from a psychiatrist before you do some thing that may cause permanent damage to your health or finances.