Beyond exhausted

I have no idea where this comes from but every so often I just can't sleep and I absolutely hate it! I will fall asleep early and then all the sudden, I get startled and wake up...it feels like EVERY muscle in my body is tight and sometimes have shortness of breath and I just can't get relaxed...

I have no idea what this is from...I'm not stressed about anything (that I'm aware of) I am thinking of starting yoga and maybe even meditating to just relax...I have started to walk every nights in hopes that will help as well but it's not an every night or even every day thing that happens but when it does it is HORRIBLE and I am just beyond exhausted and just am trying to wrap my head around what it could be...

Has anyone else experienced anything similar or know of anyone that has experienced this