How do I tell my girlfriend it's not her

My girlfriend has been feeling like I'm drifting apart from her lately because I don't pick up her calls as much and don't respond to her text as soon as I should. She's also been trying to come over and I've been telling her no lately. Truth is I'm depressed as hell. I don't know why I just get like this sometimes to were I don't want to talk to anyone and just want to stay in bed. I'm barely making it through work and even called in yesterday. The reason I haven't wanted her over my house is because my house has gotten so cluttered it's gotten out of hand. I'm too depressed to clean my house but I'm also depressed my house is dirty. I don't have a single dish in my kitchen besides pots and pans. They're all in my room and I haven't even been eating lately so idk how I even have all these dishes. She feels like I'm pulling apart from her and I'm not trying to. It's really not her.