How can we say spontaneously in a natural way in Japanese?
Here the context: My German friend will spontaneously visit Okayama tomorrow. Because of that I want to cancel our running session tomorrow.
I want to express that someone decided something on short notice. It wasn't possible to predict it or plan in advance. In English I see this as a soft excuse for the cancelation mentioned in the example sentence. Spontaneously fulfills this purpose. Can a Japanese word do it too?
My (Japanese) language partner recommended the following: 自発的に --> Literally means spontanous. 彼は自分自身で岡山を訪れることを決めました。--> In the context of the example a good way of saying spontaneous is 自分自身. Can you confirm his recommendation?
Thank you in advance for your kind help :)