I felt a Funeral, in my Brain Questions

Bring on the tough stuff - there’s not just one right answer.

Have you ever felt like there was another whole world inside your body or mind?
Why does the speaker keep hearing repetitive sounds like drums, bells, and footsteps? Do these sounds correspond to something in her body or the real world?
Who do you think is inside the casket?
What kind of the experience is the poem trying to describe?