Britt,
I am very sorry to hear of your loss. Although not exactly the same, I lost my dad when I was 25. He had diabetes, high blood pressure, kidney failure, congestive heart failure, loss of legs and fingers, etc.
I came in late one night and instead of checking in and saying good night to hi, I just went to bed. I was awakened the next morning by my mom asking me to check on him. He was gone (lying in the only comfortable position he could get in).
I guess you didn't need to know all that, but just for me to say I know a bit of where you are coming from. From that point on I continued to gain weight. Ultimately, it was my wife Diana (whom I met about a year later) who inspired me to get healthy.
At this point, you need to rely on the important people in your life who are still here. Yes, mourn for your dad, treasure the time you had here with him, but make sure that you take care of yourself.
As someone whose goal is to help others by becoming an EMT, you know how important life is. Remember that. Cling to that. Lean on the people here and others in your life.
Start Medifast. Its only going to make things better.
I hope my words help you.