My father died april 8th, 49, natural or not?

hello my father worked for the plants, he coordinated natural gas underground cavern storage drilling, well thursday april 8th he got woke up in the middle of the night, round 3am, he was in the plants, there was a gas leak somewhere with his equip, he went and helped a guy fix it, he held latter while guy tightened bolt for around 45 minutes, he said he was really worried about his lungs, cause they were burning, then he was having cold sweets while he was holding that latter, got him really worried, he came home later that morning cause he couldnt go back to sleep after, his back was hurting really bad, and he was worried about his lungs, my mom put cream on his back to help and at around 6pm april 8th he took a nap and died in his sleep at around 8pm, wondering what caused it and if in your opinion could it be related to this gas leak... he was 49 yr old never been to the doc for anything, but i know he had sleep apnea... dad told my mom all this before he took a nap that day they were gonna go to the casino at 9 and have a little fun