Beardie attacked

My guy is 4 months old, big sweetheart and a bit too curious at times. He's nipped me at times when I was handfeeding him, but I wouldn't call them a bite.
At my old apartment I would take him out a little before bed or on nights when after the lights went out he was restless and he'd pass out on me. Its been a week since we moved, showing no obvious signs of stress, and last night I took him out after turning off his lights to come lay with me because I was having a rough day and more importantly I thought he'd enjoy it. He just laid there for a while on my chest staring at me, which is pretty normal for him. I was just letting the back of his head, then he started gaping a little. I hadn't seen him do that but in my tired mind I thought he was relaxed. Shortly after he lunged at my face, latched on hard to my upper lip and drew blood. Never has he done anything like that before.
I don't blame him at all, I know 100% it was my fault, but I'm still bothered and a little upset that it happened. It was our routine yet all of a sudden that happened. He wasn't showing any other signs he wasn't happy, maybe he was just being curious? Any advice on what to look for in the future?

do you wear glasses?

Yes. I don't think I was wearing them at the time but I don't remember 100% if I was

most likely you were, and he saw his reflection and thats what triggered it, especially if he was winding down for the night

my buddy does the same thing on occasion, even though hes nearly 4 years old, and knows there aren't any threats to him, he'll see his reflection in my lenses and goes for the bite. its just a reflex at what seems to be a sudden intrusion by an enemy beardie. he quickly realizes there's no threat and goes back to snoozing.

i wouldn't worry about it unless it becomes a more frequent occurance

That's a good point. I am going to try seeing if my young beardie is less skittish if I have my glasses off.