Leo seizes up when held?

My leopard gecko has always been quite adventurous when I take him out of his tank. Although the last couple of times I took him out he would cruise for a bit, but then seize up. He doesn't like being pet, but this time he didn't even move when I tried, and when I picked him up he was completely still, and somewhat stiff. When I put him back in his tank he returned to his hide, and moved as usual. I was unsure if this would be a cause for concern, or possibly he was just severely frightened? Has anyone else had these experiences, or possible explanations?