I did 3 nights 4 days away in Cornwall (I live in London) on my own. I felt zero guilt and it was amazing to just have some time to myself and recharge.
I'm planning to do this in the next year or so. Nothing fancy just a night in a premier Inn to sleep!!!!
You shouldn't feel guilty, I know it's easy to say but you need to rest if you can go for it and you'll come back better to look after them
I've done it as a parent of an autistic 4 year old. You can't pour from an empty cup. Go and have the rest you deserve.