After that tiresome long journey, he felt drowsy.

Answer: Option A

Sluggish : lacking energy or alertness.
Irritable : having or showing a tendency to be easily annoyed.
Energetic : showing or involving great activity or vitality.
Dizzy : having or involving a sensation of spinning around and losing one's balance.
Drowsy : sleepy and lethargic; half asleep.

Synonym of Drowsy is Sluggish