My boyfriend isn't texting me back?

I have been dating my boyfriend for almost a year now and we talk almost everyday. Last night he sent me a message saying "I need to talk to you...". (I didn't get the message til the next morning). I replied saying "What is it?" and he hasn't texted me back at all since when he sent that message. I'm very worried that a sudden break up might come up or that he is mad at me for something. I don't know if his phone is on or if he is busy because I don't have my cell phone to call him. Please help me!