You dont suddenly go blind from diabetes. It takes decades of struggling with diabetes before it affects your eyes and it takes even more time before it causes blindness and by time, I mean years. Believe me, if you had diabetes to that point, you would have known by now because you would have had serious medical issues not relating to your eyes. Diabetes is not hard to diagnose.
As far as eye diseases that cause vision loss are concerned, they also take years to get to that point. You would know far in advance that you had a serious eye disease leading to vision loss.
You don't suddenly go blind unless you are in an accident or have some devastating brain injury of some sort. The only conditions that make you temporarily blind, are migraine related and by what your describing, that's exactly what's occurring to you. The sudden vision loses and seeing "shadows" are classic symptoms of ocular migraines. I get them, they have made me blind before but it temporary. Your vision returns even though its incredibly frightening.
Floaters are normal and not indicative of blindness. Just because someone you know has a condition where they only see red light, does not mean that its a precursor to blindness. I am sure many have lost their vision and haven't seen red beforehand. Ocular migraines do cause large floaters of different colors in your vision. I don't believe these are true floaters, they are just a symptom of the migraines. I see blue ones but have also seen purple and red though white is the most common.
Keep in mind, migraine is a neurological condition, benign, but it does not always manifest with pain. Most of my migraines are completely painless. So you don't need to have a headache to have a migraine attack.