Guys I think i like my best friend

uh so she's a girl.. im a girl. I dont know everytime im next to her my chest starts pounding like im abt to die.. TT is this like a normal thing for everyone.. The thing is this all happened when she told me she DID like me for a while and was too scared and tried to distract herself, and it worked (she said) but after that we've been acting likee actual couples, even my friends are doubting.. IDK WHAT TO DO IM PANICKING TT