A 32-year-old man is brought to the emergency department after a motor vehicle collision. He was unconscious at the scene for approximately 5 minutes, then became alert and lucid. He was discharged from the primary health centre with reassurance. Two hours later, he develops severe headache, vomiting, and loss of consciousness. CT head shows a lens-shaped hyperdense collection in the left temporal region that does not cross the midline. What is the most likely diagnosis?