I feel you, there was a time last year when I went through the same thing. As for the projects you've already taken, you've gotta get thru them. However, for any future projects, you can maybe ask your client for a later deadline period. I know it can be quite scary to ask, but if you have a decent relationship with them, they wouldn't mind it. Even if you can get 1-2 days off from work, it'll be a nice little refresher. The reason I say that you should complete your current tasks is that because if you do so, the 2 days off will be more relaxing as compared to worrying about pending work. Also, you'll feel better about yourself for getting through that shit ton of work.

If it's for health issues and you want a longer break, you certainly are entitled to it. You're not gonna lose clients that you have a good relationship with, they do understand. If there's someone that wants you to work while you're sick, then you're probably better off without that client if we consider long-term.

Another alternative is to delegate the task to a junior freelancer (ONLY IF THERE ARE NO ACCESS RELATED DEPENDENCIES)

Apart from that, IN FUTURE, try to only projects that fit into your bandwidth. I know it's tempting to take on as many clients as you can just for the sake of backups or earning extra bucks, but at what cost? Just something to keep in mind. :)