Was it overexertion, dehydration or both (exercise question)

I went for a 35 minute run, yesterday. First time that I have worked out like that in a long time. When I was done, I could barely form enough saliva to spit and my mouth was extremely dry, it was hard to shallow. I didn’t drink water until I got home. Like an idiot, I drank two cups of coffee at 8 in the p.m. Four hours later, I get a splitting headache. Worse headache that I have ever had. I take some Ibuprofen and go to bed at 10. Headache goes away after an hour, but, then there was nausea and vomiting.

What happened? Did I overdo it with the exercise right away or was I dehydrated?

What can I do next time to prevent this from happening?