I'm so excited to go to a concert i feel sick

The title is so vague. Just listen: I unexpectedly in the course of 1 day got news that I'm going to see my favorite band live twice next month. I'm front row both times and yes, it's happening during the pandemic. Understandably I am very excited and nervous. I never saw them live before and they're my heroes!
Well I don't know why, but I suddenly am deeply physically stressed out by this. Mentally, I'm purely happy. Maybe a tad bit nervous. So all don't know why I feel so freaking nauseous 24/7. I lost my appetite days ago and I'm 3lbs away from being underweight according to my BMI. I can't afford to not eat but I truly lost my appetite. I'm becoming too weak to focus at work and my sleep is just... interrupted every night. I feel like I'm falling apart and whenever I think about the band, the sickness intensifies. I'm so in love with them, is really all I can conclude. I'm just confused because they're just normal people and I've been to 19 concerts before. Why am I losing my health over these shows? I seriously don't understand why being happy would cause my body to react so sharply. What do I do to calm myself and eat again? How do I relax for these shows so I don't wind up fainting or something? Most importantly, is this all just stress and am I overthinking without realizing?