Hi. I’m so very sorry to hear about your dad. My first trip back after I lost my mom, I went into MK knowing that I was going to probably ugly cry as soon as I saw the Castle… and I did. But for me, it was also healing, to be back in one of her favorite places on earth.
She only had happy memories at WDW, and I stop on her special “spot” every time (Disney handy-dandy marked it with a survey marker in the pavement

) and blow her a kiss. Not gonna lie, even now - more than 12 years later - I get emotional for a moment. But it is followed immediately by a sense of comfort, because this is where she would be if she could be. With us, on vacation, laughing and having a great time.
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With or without a DAS, technology is your friend now. There are all sorts of things you can consider (maybe discuss with your therapist?) that might be helpful.
@Mirabell Rose mentioned headphones - even inexpensive noise-cancelling headphones (in-ear, over the ear, or bone conduction are some options) can help make your auditory space feel less crowded. Some can affect how area music, and parade music, as well as ride/attraction music & other audio sounds, so take that into account.
One of our family members now uses
Loops, and they have proven to be very helpful at Disney World. She can even stay for fireworks at MK now, something she has not been able to do for quite some time.
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If you find that you are unable to speak, technology has you covered here as well.
We have a family member who has anxiety, and everyone who travels with her has an app on our phones called "Emergency Chat". The logo for it looks like this:
It's an app that will let you text someone when you are too overwhelmed to speak.
You can customize the opening screen (shown below) to help give the person you are communicating with more information.
You "text" with the other person, by handing the phone back and forth so you don't have to try and talk when you are not comfortable with speech in the moment. It's just another tool to have ready (like knowing that you can use First Aid at the Parks) in case you need it.
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Disney is going to help you also: the My Disney Experience app has so much useful information for while you are in the Parks; not just maps (but handy!) but also wait times for rides, menus for dining venues, and so much more. There are far better posts covering the use of the app than I could muster here, but it is a great tool, and I highly recommend it.
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As great as technology is, there are other things to consider.
Every member of our family always carries small individually wrapped alcohol swabs (my hubs is a T2 diabetic, so we always have plenty of these around) in case someone needs them. They are particularly effective on helping with nausea, but can also help when someone is feeling anxious; somehow the smell just “grounds” them.
Additionally, we all always have Extra-Strength Tylenol. Tylenol is particularly good at not only relieving pain, but for some people, it can help calm them if they are headed for an anxiety attack. Take 2 with plenty of water, and ideally a lil snack for the tummy.
Create your own privacy - grab a hat or a simple scarf (or a favorite hoodie) as well as a large pair of dark sunglasses. Using your headphones, wear the hat/scarf plus sunglasses (or hoodie + sunglasses) and you have created a private “zone” just for you that no one can really intrude upon.
Remember that First Aid (in every Park, marked on the map) is always your friend. Here you will find some of the nicest CMs at Disney World. You can ask for (generic) Tylenol, use the restroom, lie down for a bit, and cover your eyes (pending availability of cots) or just sit with trained professionals nearby in the relatively cool, calm atmosphere.
If you have the time (any maybe even if you don’t) try to build in some time for a “reality break”, and get out of the Park(s) for a bit. Go back to the Resort, and have a swim in the pool, or head to Disney Springs and grab a Starbucks you can sip from a quiet spot. Go see a movie at Disney Springs, or do some Resort-hopping, and visit some of the hotels; use any of the Theme Parks or Disney Springs as a hub to ride to any Resort hotel at Disney World.
Last but not least, I would certainly consider staying on property if I were you. That way, you only have to grab Disney transportation to get back to the quiet and privacy of your own hotel room; you won’t have to try to drive when you are potentially upset or overwhelmed. Consider a quieter Resort (if you can afford it) like POFQ in the moderate range, or WL or AKL in the Deluxe range.
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Take tissues; Disney makes us all emotional on a good day. Go say “hello” to the Tree of Life, and wave to your dad for all of us too. Carry his joy with you, and try to remember to act your shoe size, not your age. Disney is for the child in all of us; I hope you get to play and truly enjoy your vacation