Please help. It's about my dog?

Okay my dog has been coughing a lot and sitting in her bed all day shes usually really hyper and crazy and stuff so yeah. shes a black and white er annd shes eight very close to nine. I love my sadie with all of my heart and soul and she is my first dog and only dog i have ever had. i love her sooooo much and i am soooo worried about her. what should i do. i told my parent and they were all making these jokes bout how shes gonna die and then my mom is all like she is fine dont worry but im scared. help.