Seriously?

Thursday night on Grey's Anatomy, we find Izzie having a meltdown by continually seeing her late boyfriend, Denny, in the halls of the hospital. Now, it wouldn't be a problem if he was late as in timing, but in this case, he's late as in deceased. Izzie has seen Denny at the hospital before, so it's understandable she might see him again, but Thursday he followed her home and encouraged her to touch him so she would know he was really "there for her". Izzie touches and then falls into his arms for a make out session while Alex is conveniently in the other room burning Denny's sweater. Seriously? Making out with a ghost? Isn't that a bit awkward? What happens when Alex comes back into the room and her arms are around nothing and her mouth is going to town all on their own? Ok, there has been some buzz that perhaps she has a brain tumor and is experiencing hallucinations. I'm hoping for a good explanation, because this is getting a bit far fetched and it's not The Fringe.