Summarize the following:
It may be that he has retreated just to gain some space if you've been too intrusive or intense of late. Maybe you're texting him often, or you've been calling three times an hour for the past three hours. Understand that guys generally appreciate their space and not having to be with you 24/7. There are a lot of very authentic reasons that might seem as if he is "ignoring" you, but actually, have nothing to do with you. He may be busy. You may have the habit of talking daily, then suddenly it stops, and you urgently want to chat. It has been a day, but you're frantic. And he, well he is very busy! When he's busy, you can expect him to cut off the communications until the task is done. He doesn't feel well. He has been trying to deal with a head cold, a shoulder pain or a stomach ache. Being the stoic that he is, he has only stopped replying because he doesn't want to burden you with his pain or let on that he doesn't even feel so great. He is tired. Genuinely, pooped. He just wants a bit of space to recover his lost energy, so he's withdrawing for a week of snooze catch-up. He has experienced a family issue. He is uncomfortable talking to you about it because he has issues with his crazy/possessive/insane/angry/moralizing/whatever family and it's just all too hard to go into the gritty details. He'd rather you didn't get involved because once you are, awful entanglements will ensue. This can be a very protective stance, both ways. He has hit a snag at work. The deadline is looming, the boss is breathing down his neck, the job's future is precarious. He's salvaging what is left of his work opportunity, and you are suddenly a distraction.

Summary:
Consider whether you might have given your boyfriend cause to feel overwhelmed. See things from his perspective.