Dwarf Lionfish question

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I've got a lionfish from Dwarf Zebra. I've had him now for nearly a year. The last 2 -3 weeks, he has been acting weird. 3 weeks ago, when it was feeding time, he would come to the front and took 3 lance fish only (fed 3 times, ate same each time), then settled back to his normal spot. 2 weeks ago, he took 2 krill at 2 feedings, and 1 lancefish at another.He's not even come to the top for food this week. He's staying in the back of the tank, and he didn't even recognize it today when I put the food on a feeding stick and put it right in front of him. Is it normal to go without eating a lionfish? I'm worried that he is sick and dying, and I don't want to lose him.