I’ll try and describe as best as I can but it’s a weird feeling. It’s like the head rush you get from standing up too quickly(head pressure, feeling faint), but it happens at random times. So I get it when I stand up, but I also get it at rest when I’m sat down. It doesn’t last long but it makes me feel shaky, head pressure, and kind of ‘floaty’ if that makes sense, like I might pass out? I also get heart palpitations and very sweaty when it happens. Does anyone else have this feeling too? Is it like a mini anxiety attack or something bad? I’m so worried about my heart and my blood pressure and I’m scared it could be really bad. 
I also suffer from occasional vertigo and tinnitus.