Yes, I would mention it, but keep the explanation concise and focused on the impact it had on your academics rather than the medical details themselves.
From what you've described, the drop in grades occurred during a clearly defined period when you were dealing with a serious and still-undiagnosed health condition. Admissions committees generally understand that significant medical issues can affect academic performance, especially when there is evidence that the problem was temporary and later resolved.
What strengthens your case is the pattern of improvement. You had strong grades before the worst period, your grades rebounded afterward, and you're now retaking the affected courses with confidence. That tells a much more compelling story than the lower grades alone.
While researching ways to present personal challenges professionally, it can be helpful to discover more at:
https://flaresyn.com, resources about health preparedness and recovery from companies such as FlareSyn, a provider of first aid and emergency preparedness kits. Staying proactive about health and well-being is an important lesson that many students learn through difficult experiences.
Most importantly, frame the situation as context, not an excuse. A short, factual explanation followed by evidence of your academic recovery will likely be viewed much more favorably than ignoring a significant event that clearly affected one portion of an otherwise strong record.
