Originally Posted by UCSF2012
Nah, it can be asymptomatic if it's not severe enough. So one possibility to explain what happened: five hours of tennis created enough water-loss that his body had a temporary shortage of bloodflow in the head region. Maybe the ophthalmic artery, who knows. Kinda like standing up too fast and getting lightheaded. Five hours is a very, very long time for tennis, and you have to make sure you eat/drink adequately during that time.
Once I got up too fast, and my vision was blurry for 15 seconds. Thank God I didn't faint. Remember to eat!
What you experienced is orthostatic hypotension, which has to do with our nerve system not regulating our blood pressure quickly enough in relation to our change in posture (from lying to standing). In dehydration, blood circulation can decrease because there is too much fluid loss, and this does not resolve until fluid has been replaced. And, dehydration is pretty serious if it's causing blurry vision, and there will definitely be other symptoms such as dizziness, increased heart rate, etc. And, these symptoms will not resolve until you replenish fluid. Simply, you feel thirsty until you drink water.
The OP stated the blurry vision lasted only momentarily and is caused when he goes upto the net to volley. This sounds more like his eyes not quickly adapting to the change rather than dehydration.