Long swim and being disoriented

I found using ear plugs helps me from feeling like this after a long swim.

Not sure what you are referring to. Vertigo? Yes, that can be common after a long swim. Some people find that ear plugs help. It's also more common with open-water swimming. If you felt weak, light-headed, and exhausted, maybe low blood sugar? That's a long swim for most people. Maybe you needed more fuel before you started, or a snack right after finishing. I know I really need some food right after any workout of 3000m or over. You may also have paced too hard if you just swam your usual 1500m pace.  Finally, mental stuff? 3000m non-stop can be kind of mind-numbing. My craziest experience was swimming what I thought was 1500m in what turned out to be a 3000m pool (while traveling). Kept wondering why every length was taking so long, why I felt so tired. I'm a strong swimmer and just couldn't get what was wrong. When I finally got out (after about 55 minutes), I felt exhausted, muscle cramps, lightheaded, etc. Was halfway thru my shower before it suddenly dawned on me I'd just done 3000m, hard!  Too much staring at the black line rots your brain, I guess. 

Thanks, I will try the ear plugs and also take a closer look at nutrition before and after. I probably wont be doing that lenght often, just wanted to see how it felt. Im new to swimming and wasnt sure if this was normal. 

Ear plugs.

+1 on the earplugs. I wear them for every race and during long swims and it solved the getting dizzy/disoriented problem.