I’m experiencing Dizziness with Metastatic Breast Cancer

I have MBC dx in June 2018 with Mets to bone and lymph nodes. I have began to get dizzy the past 3 weeks. I am having a brain mri Monday and my last one was in April and all was clear. I have been stable on my first line of meds since dx. I’m freaking out, I have a 7 and 8 year old and I can’t imagine telling them things are getting worse. I’m just so scared, not so much for me but for them.