Unexplained Death

Question:
 My 8 month old kitten/cat passed away yesterday. I am naturally grieving & overwhelmed with guilt. I have been researching sudden deaths endlessly and cannot find any solace whatsoever. I took him in after he was abandoned at only 5-10days old. After many trips to Petsmart and internet research, I thought I had done everything right with one exception. As his first medical examination approached, I was hit with some unexpected major finances. Here I am months later and still struggling to make ends meet and needless to say, he had never been seen by a vet. He was spunky, energetic (extremely-he climbed the walls all the way to the ceiling!), loving, and appeared in great health to me. Monday morning when I returned home from 3rd shift at 7am, he appeared lethargic, was crying and shaking. There were no abnormal stools, vomiting, changes in appetite, aggressive behavior, sneezing, coughing, feverish, or other visible symptoms. I mistakenly assumed he was going through his manly changes, or had perhaps caught my cold. I warmed him up in some blankets, put the water in front of his face (which he drank), and gave him some love. He stopped crying and walked out of the blankets. I planned on taking him in to the pet hospital if he still looked bad when I woke up. After I slept about 6 hrs, he appeared much more lethargic. I immediately fumbled through the phone book searching for the nearest clinic. He died before I even got to find the page. I am devastated!!! Rather then expressing the depth of my self-blame and saddness, I'll advise you of some possible additional causes that I think may have contributed. He would sometimes hang out with me in my attached garage. Perhaps he found a mouse or got into something poisonous? Sidewalk salt? Gardening agents? He has escaped outside twice without my knowledge, but not since fall. He also preferred human food over cat food and always tried to eat it, sometimes succeeding if it wasn't concealed well enough. Lastly, could the frequency of litter changing participate? Obviously, if I had the money for a post-mortem examination I would've gotten my kitty his shots. I'm also well aware that without one, there is no definite diagnosis. But if you can provide me with any feedback on the concerns I've expressed, or narrow down some information, it would be sincerely appreciated. PLEASE HELP!
Answer:
 Anti-freeze, many house plants, cleaning products - lots of things could have poisioned him. Could have been a heart condition. What difference does it make now? If you are expecting someone to come up with a definative answer saying it wasn't your fault, well, no one is going to be able to do that. Necropsies are often indesisive also, so that may not have given any reason even if you'd had one done.
Answer:
 I'm sorry for your loss :( try not to blame yourself, the cause was fatally serious - he may not have survived, even if you had made it to vet. He was very young and may have had serious underlying condition from birth. I did everything I could to try and save my dog when he developed breathing problems, he was on meds and I took him to my vet twice within days of him collapsing and dying in my arms on his 9th b'day :( I'll never know for sure exactly what happened. It's been 18mths since I lost him, I miss him every single day, the guilt very slowly subsides. I really hope you manage to find some peace.