Carry On!
And how to get oneself out of an "existential tailspin?" Exist. Carry on. Take one step, then another. Gaze at the sky, or the lake. Watch the clouds, or the waves. Focus on something. Something small. Play your guitar, work on a song, or a new riff. Cook a meal. Eat. Divert yourself. Think about someone, or something, besides yourself. Exist. And forget that you exist.