Late Return of PIP form

Hi, I'm a new member and not very clued up about hows forums work so I apologise if I'm doing this wrong. My current DLA award ends in August so when I received the first letter a while back about needing to apply for PIP I was really thrown cos I thought I had more time, since then everything has happened so quickly i'm struggling and now panicking. I've only just realised that the form is due on the 8th May. I'm a stroke patient with fibromyalgia so I find things like this very difficult at the best of times and usually have to do them in very small steps but the last few weeks have been spent mainly in bed, firstly with a viral infection that floored me and then just when I had been getting back on my feet for a few days my back went into spasm last Wednesday and I only got back out of bed , still very stiff and sore , on Tuesday. I have just been attempting to wade through all the correspondence and realise there is absolutely no way I can get this completed and sent in on time. I admit they have sent me reminders by mail and text but that just stressed me out more when I was unable to do anything about it, although to be fair I really wasn't aware that the 8th of May was so imminent. So i'm wondering if anyone here can tell me what I should do now ? Should I phone them and explain, can they stop my money ? Or should I just not bother speaking to them and get it done as quickly as possible. Any advice would be very welcome please ?