bad cold at night

Da
My LO has had a cold for about a week. But it seems she's barely congested or coughs during the day but at night she can't sleep and throws up her feeds with mucus in them. We thought it was because she was laying flat but tonight we had her in her bouncer chair which she's been napping in during the day. Why is her cold worse at night then? We do have a humidifier in our room..but I can't think of why that would make it worse... Any ideas?