Welcome to the forum and thank you for sharing your experience . . .please accept my sincere thoughts about the passing of your grandmother . . . this is a difficult situation even for those without anxiety . . .
A lot of your symptoms could be anxiety related . . . you went to your family physician which is super . . . that's always the first step and you are seeing a therapist which is great and that is the second step . . .
It is indeed scary . . . . you have a history of anxiety and it * might * be that there are unresolved issues and something triggered a new episode for you . . . it appears that you may even have a predisposition to anxiety and panic attacks . . . add to that (and this is me also) that you are preoccupied with illnesses and dying . . .given that your family history has had stroke, cancer, and MS, you probably fixate on these issues . . . I have the feeling, and I am not a med professional, but I have a feeling that your grandmother's illness and passing may be a trigger for your current episode . . . and you are overly preoccupied, from an early age, about people becoming ill or passing and leaving you . . .
Personally, I do not think that you are losing your mind . . . .I think that you are struggling to recover from an episode of anxiety where your worst fears have, in a way come true from anxiety's perspective with respect to the health of your loved ones . . . .it is not unusual for anxiety to become more pronounced at night . . . things are quiet, the mind is trying to sort through the day's issues, and anxiety gets to have pretty much a free area to roam around . . .
One strategy, and one you already recognize, is the benefit to externalizing your thoughts and your feelings by writing about them . . . this helps to put them into reality and to start the process of de-emotionalizing the anxiety . . . you also seem to be engaged in anticipation anxiety . . . you are projecting on to the future what * may * happen and this just adds fuel to the anxiety . . .
My suggestions and they are only suggestions are the following: try mindfulness to relax your mind at bedtime so you can get sleep --- lack of sleep increases anxiety for me; eat something even if you are not hungry --- if you do not eat, then the brain does not have the appropriate nutrients and the lack of nutrients may affect the brain's chemistry and enhance the anxiety - even if you have to eat small amounts of food 5 or 6 times a day, make healthy choices but eat; I know that you are probably tired, but get out and walk . . . it can be 5 minutes in one direction and 5 minutes back --- do something for you; keep a journal or come here and check in with us and let us know what is going on . . . get your thoughts out so that they become embedded in reality and you can deal with it; and, this is perhaps the most difficult of all, don't engage in anticipatory anxiety . . . go one day at a time --- be with your 15 year old, rejoice in your house, spend time focusing on the good things that are in the here and now and not what might be . . . we just don't know what the future holds . . . . I know this is difficult . . . it is a process and not an event but you need to deal with your triggers which a therapist can help to guide you and you need to refocus and take the power away from the anxiety . . . you have the strength to recover but you need to embrace the process . . .whichever one works best for you . . .
So, your physical health is fine so now you need to focus on recovering your mental health . . . your Dad's life history does not have to be yours . . . learn from him, by all means, but do what will garner you the best effects for you and your daughter (let her know what is going on so she doesn't think that she has done something "wrong" --- perhaps even enlist her to get you out for a walk . . . it might be a time to share some chatting --- and, by all means, come here as often as you feel comfortable . . .we're a pretty good community at supporting each other . . . take care, kc