What do I say to a friend who I had one night stand with recently?

You did the right thing already. You called him and left a friendly message and asked him to call back. If he is interested in you (and if he respects you) he will call you back. If any fruit will come from this, and if he likes and respects you, he will call you back.

If he doesn't call you back, leave a message one more time, and he should have no excuse as far as not getting any messages. And he should not have any excuse for not calling you.

If he doesn't call back after the second message; he's not interested and he's rude and disrespectful.

Define casual friend----is this somebody you normally hang out with on occasions, or do you barely see him. It seems to me he is behaving like he just wanted a sexual date, and now that he got what he wanted, and now he has done a houdini act. Otherwise, I don't see why he hasn't called you or returned your messages. Perhaps he is thinking that you want something more? Hard to say.

Oh wow. Not hearing from him is not such a good thing. I believe you know that deep down inside too. I have kinda been in the same situation (other than going to his place) Had a few drinks with a guy danced the night away (not an ideal first date) haha. But it was fun! He text me and told me he had fun that night as I got home. But I did not hear from him for days. So of course us "girls" our minds wander. We want guys to like us esp. When we "like" them. I decided to text him mid-week. As you decided to call him. I got a response saying his week was really busy. So I just left it at that. . I asked a (male)friend of mine at college about it. He said " if a guy was really into you. He would call you and contact you after" It stung pretty badly but I do believe that deep down inside. I just needed to hear it. : ( it really sucks.

I mean he could possibly surprise ya and call you or something but usually if a guy is really into someone he will make it known to the world. That always feels better anyway. So go out there and find a guy that will do that : )

Keep your head up girl!
You are not alone.

He may be a little weirded out. Maybe he thinks you guys crossed the line and he doesn't want to give you the wrong impression. But it sounds like clearly you are okay with just being friends and not letting one night get in the way of that. Try explaining that to him. He be guessing too much into it, but if you really want to still be his friend, give it a couple days. Then call him and be like 1) I need to get my stuff and 2) ask him why is being so weird. Tables are turning here.