Male dog unable to stand while peeing blood

Has anyone had any experience with this type of event.. I just witnessed my 4 year old Rottweiler laying on the ground while his hind legs started convulsing. He would not come to me when I called him and as he lay there for approximately 8 to 10 mins with his hind legs stretched out and convulsing he peed in bursts with the presence of blood. I did notice blood in his urine a week ago but he was peeing normally and very active. He was very inactive all day. I massaged his hind legs and just tried to help him relax because  they were so tight it seemed like he had no control over them. So confused about it all. After about another 5 mins he finally got up and started walking again. Its night time so I cant go anywhere but in desperate need of insight into what this might be :(   Thank you everyone!

Hello!  You should be able to call your emergency vets at any time to assess a history and we would recommend this, as impediments to urination can become serious. Is your Rottweiler castrated?  If not, I wonder whether his prostate may enlarged, pushing on the tube passing through his penis.  This can be for benign reasons connected to sexual hormones but is sometimes due to cancer. Other possibilities include cystitis, cancer, urinary crystals, polyps, inflammation etc There are many possibilities but it does sound quite uncomfortable and as though it needs addressing.  Your vet will help you to plan and  differentiate between them.

Please do speak to your emergency vet tonight to be properly assessed.

Thank you, this is along the lines of what was spoken about over the phone. I will give this information so they dont miss anything. I will keep updates

Your vets who can see the dog will have much better information than me - all the best and looking fwd to hearing what they find.