Um... ischemic colitis is a circulatory problem. Acute cases are usually caused by a clot (same thing as strokes/microstrokes (the latter called Transient ischemic attacks). And of course it went away, the clot broke up or moved on. You need to switch to water. And plenty of water. Caffiene is a diuretic, which means it causes your body to get rid of water. I'd be more concerned with sodium intake, especially in relation to water intake. I'd advise water. Not vitamin water, not watery energy crap. Water. And cut salt down as low as you can.
I experienced a Transient ischemic attack (evidence suggests, but we're not 100% sure) myself late spring this year (luckily no lasting effects). Number one thing my doctor told me to do was keep sodium under 2000mg/day (it's harder than you think) and drink water. I'm down to just a soda in the morning, then 1-4 liters of water though out the day. I feel loads better overall and my blood pressure dropped to healthy levels. The caffeine drop may not be pleasant, but you gotta get off that stuff. At the very least, any addiction is a bad thing.