Writing slumps can be the worst, whether it be normal solo writing or in a RP. It's scary falling into a creative slump in RP because you tend to have people depending or waiting on you to post, and that doesn't help the anxiety, the stress or the motivation to post. And honestly, it's a mixed bag when it comes to dealing with slumps. Everyone deals with it differently, and it'll take some time to figure out what works best for you. 

Me? I usually take a day for myself and relax or find other enjoyable activities. This works especially well when i'm doing long form writing, where I can waste hours on a word doc and feel like my soul is slowly being drained out of my body. It sucks. Doing something [i]fun[/i] also helps, whether it's going out for a nice brisk nature walk, watching a few episodes of your favorite TV series or just sitting down to play a game. 

Sparking the creativity is also a good way of reinvigorating yourself-though be wary as you can burn out twice as fast if you keep pushing yourself to write/post/etc. Hitting a slump is one thing, but completely burning yourself out is another (and it can be bad pulling yourself up after that). 

Find things that inspire you, make you happy, or just relax you. If you don't have any pressing RPs going on right now-even better. You can take as much time as needed to relax and let yourself rest before jumping back into RP. If you need to take a break while in the middle of a RP, it might be good to contact the GM and other writers, and let them know what's up as well. 

I hope you can get some rest in and feel reinvigorated for writing! It's one of the most demanding, draining and mentally exhausting hobbies out there, but I wouldn't trade writing for anything in the world!