Does not running for 2 days affect your running ablity?

I have been a lot for the past month like 25 miles a week. last week I ran 5 miles at 9 pace easily. on Friday I did a mile time trial and only ran that and a 1/2 mile warm and cool down I didn't run the weekend. today I ran 3 miles which is usually very easy for me. I ran it in 32 minutes I can easily run it under 27 I stopped at the 1/2 mile mark and I felt dizzy and about blacked out. I normally dont do this I was running by myself too. also I haven't been drinking water too much could this cause running bad?