okay the first huge variable is dehydration, everything is off if you are dehydrated.
understanding how a “normal” works may shed some light, so here goes. your liver is a sugar/insulin sponge. in a normal, you eat anything and your body makes insulin. excess sugar is either burned by activity, absorbed by your liver, or converted to fat. the burning and converting chemical process needs insulin as a catalyst for every cell in your body except your brain. cool right?
so we inject an “analog” it’s not exactly insulin. it hangs out way too long. it doesn’t start as fast because it has to get absorbed through the interstitial before it gets to the blood. long-acting like lantus (or whatever) is a hugely complex chain that blocks absorption so it hangs out for 14-26 hours. your liver may dump and recharge but it isn’t always as accurate as when you can naturally make insulin.
hard physical activity is typically aerobic or anaerobic. the first is jogging the second is weight lifting to generalize. tennis can be both. aerobic tends to lower blood sugar by promoting burning to fuel the exercising muscles, anaerobic can sometimes raise blood sugar because of a complex issue of the activity being mixed with stress hormones the most famous is Adrenalin. adrenalin causes systemic increases in blood sugar because it historically is triggered when you come face to face with a hungry lion in the woods and need a little “boost” so you can evade being eaten.
so my guess from New Jersey is this: dehydration and anaerobic equals a lot of adrenalin equals high blood sugar - or - actual low blood sugar causing your liver to dump all stores. either or both of which could easily cause a huge 4 hundy. sorry you had a bad turn. I hope you feel okay now.