What possibly could be wrong with my husband, and should I be conscerned?

My husband was a young, vibrant man, full of life, but recently, he's reclusive. Four days have past, and he hasn't said a single word to me. One day, I thought I was alone in the house until I turned on a light and saw him sitting in a corner in the dark staring at me. He's been doing that a lot lately, sitting in corners, watching me in silence, following my movements with his eyes. I tried to ignore it, but I really started to feel nervous when I saw him sharping his collection of knives, which I didn't even know that he owned, a moment ago. Am I overreacting?