My ex girlfriends daughter lost her father in a similar incident a couple of years ago.
The gas heater on his house boat was producing CO2 into the cabin. He had what appeared to be flu symptoms over a period of time - when he moved off the boat to stay with family or friends, he got better. But eventually, when back on the boat he just didn't wake up one morning. Needn't have happened with a properly installed & serviced appliance, some knowledge of the symptoms and a bit of foresight.
As for your speech and language problems - see your GP and get him to refer you to the neurology department at your local hospital. I suffered severe head injury in an accident 3 years ago and one of the lasting issues is with my speech and writing - nothing too dire, just amusing when I use the wrong words. Like you, I have trouble remembering names of people, places and things and get names mixed up. Did some speech and language therapy, might help you too. But see the GP.