Today is a hot day. It is a real summer day. We can't feel comfy without running a fan. Even though it is a hot day, I haven't sold much. I have to cheer myself up by doing something else. You can't "cheer up" your mood. Your mood can become more or less cheerful. You yourself can cheer up. However, your mood is not a person or animal and that is why it cannot be cheered up.

Today is a hot day. It is a real summer day. We can't feel comfy without a fan / It's hard to remain comfortable without a fan to cool air down. Even though it is a hot day, I haven't sold much. I have to cheer myself up by doing something else.