Is it wrong to hide in my apartment during my roommate's party?

My roommate is throwing a small surprise birthday party for his husband. I was planning on hiding since I was sick, but I feel a thousand times better now, and I went to a movie and dinner with a friend yesterday. But, I still don’t want to go downstairs for this party. I saw my roommate already and gave him a birthday card and such.

The friends that are coming I’m familiar with; I’ve lived here nearly three years already… but I guess because the party is in my home, when they have gatherings I get a little agoraphobic and prefer to stay upstairs. That’s fine for a regular old get-together, but this is a birthday.