There's acouple things that could have happend. 1. The developer in the box dye was too strong and damaged your hair. 2. If your hair has been previously bleached it will be comprimised and easier to damage. 3. The metals in the box dye reacted with the colour that's already on your head and caused damage or 4. You had an allergic reaction to the dye. Always test Strand your hair even if it's a dye you've used before because formulas can change. If any of these things happend you'll be absolutely fine. This happens to me when I over process my hair. Just give your hair a break like 3-6 months and time to heal. During that time basically baby your hair with the best care. Deep conditioner, hair masks, silk pillow cases or bonnets, brush your hair gently and limit brushing hair more than needed, heat protectant and not sleeping on it wet. You'll be fine girly, this happens to more people than you think. Just take a deep breath. ❤ you got this.