A stroke, or a heart attack come to mind.
Hypertension commonly causes headache. Hypertension is a major factor in stroke and aneurysm, heart attack, and heart failure. Hypertension can lead to confusion and dementia. Hypertension can cause kidney failure; or it can be the other way around, kidney failure causing hypertension.
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them