Hi Friend,
So sorry to hear of the sudden passing of your Dad. My husband's brother in-law died of a massive heart attack 8 yrs. in front of his wife and 14yr. old daughter. It was very traumatic for them too. I personally lost my brother to alcohol poissoning last April and they think it was suicide.
Like the last poster said greiving is hard , but it's something we all have to do in our own way and time. Probably, at the time of your fathers death, you were trying to be strong since you were the older child. But when we hold it in, sooner or later it has to come out. For me greiving was like waves in the ocean - sometimes they were strong, relentless and other times calm where good memories would creep in. Although grieving isn't something any of us want to feel, it is a necessary process that helps us get to the other side. Try not to resist it and be kind to yourself. I hope once the waves of greif pass you will be in a peaceful place. Take care.