8 years ago I was 17 going on 18 when my dad woke me up for a phone call. I was grumpy so I snapped at him to get out of my room. It was work calling me in early.
I hopped in the shower, got ready for work in about 15 minutes, went to his bathroom, and knocked on his door. I could hear the water running softly in the bathroom sink and I called out "Heading to work, Dad! I love you! Call you when I am off."
When I came home many hours later my step-mother was trying to pick the lock to his bathroom and the water was still gently pouring just as it had been when I left.
If I had not been in a hurry or really tried to get his attention maybe I could have saved him from the heart attack that struck moments before I knocked. I was CPR certified. I doubt it yet always wonder if he heard me calling out as he died. If he was scared as his only hope...I can't continue or I will cry.
Get yourself grief counseling now. Not later and not "when [you] can afford it". That is your current priority for your self. Hug your mom, tell her you will help in every way you can and follow through to the best of your ability.
If he had life/medical insurance through his work you will need to contact his work to inquire about procedure. Many places will require a death certificate where others will not. From internet bills to bank accounts just know you will need it ready for some.
If he did not have insurance through work you can pay a fee online to have it researched if he had a policy or you can do the legwork yourself for free. Google can help you with that but if you have trouble in the comic weeks I can possibly help out a bit. My grandmother (dad's mom) is going into hospice and has congestive heart failure so I will have to prioritize my family first but when we get through this I would be happy to help you locate resources. If you need to reach out PM me and I can send you my e-mail address. I am out of state with limited access to a computer currently so until my family is taken care of I may be slow to respond.
The pain never quite goes away and the regrets and guilt will always be there. But with time they will fade to a whisper amidst the roar of good memories and love.
I had nightmares for a while about how I found my dad. His physical appearance was overwhelming. I suggested grabbing some physical photos of him with happy memories surrounding the photos and making them very visible and available to see frequently. If it is too much to handle for you personally don't be afraid to put them away but do understand that crying is healthy. It is okay to feel sad and guilty. Just know that it is absolutely not your fault. We are all going to make it.