You definitely don't belong on the Uboat, then. Especially if you are still diving so infrequently that you need to rent gear.
The difference is cold, dark, very low vis (we're talking 5-10 ft or less at times), high stress, higher breathing rates.....plus it's a wreck, which by definition means there is tons of stuff to snag on you.
Do your first cold water dive somewhere shallow...work up to something deeper. The Poling would be a good intermediate level dive after you've done a few shallow cold water dives. Once you figure out how the conditions affects you, move on to more advanced dives.