When you're feeling scatterbrained, you're confused and rattled. Many people feel a little scatterbrained when they first wake up in the morning, before they've had their coffee.
The adjective scatterbrained is perfect for describing someone who's disorganized, flighty, and maybe a little silly. A scatterbrained teacher might spend ten minutes looking for his glasses before realizing, to the amusement of his class, that they're on his head. You might feel scatterbrained if you show up for an appointment on the wrong day, and you can call yourself a scatterbrain. Both words have been used in English since the mid-1700s to describe easily distracted people.