Sub drop after first time meeting

I (f27) am a sub who just met a potential dom (m27) for the first time. We just got coffee and went back to his place and just sat together and we were a little intimate but nothing crazy. It was really nice and I really like him and then I went home and two days later i started experiencing the biggest sub drop I’ve ever experienced. I feel physically ill and mentally exhausted. I told him and he said it’s okay and we’ll just take things slow and ease me into things. I’m trying so hard to pull myself together, I’ve bought easy healthy meals and I’m going for runs and I’m trying to focus on work but I still just feel so unwell. And I feel so bad about it because like I said we literally just met; so I feel ultimately guilty telling him I’m still doing terrible because I don’t want to put so much on someone who is still getting to know me. Especially since this was just supposed to be a casual fwb dom/sub situation (which is still what I want) Any advice appreciated :)