For some reason I get the feeling that your mobs keep spawning near me while I'm not looking. For example I'm in the nether, just building a bridge, and suddenly I'm getting f###ed by a Baphomet from behind. I'm pretty sure I should have seen it if it was there beforehand, and this has happened on multiple occasions. Is that intended? I don't have a problem with hard mobs, but it would really be better imho if you could prepare in advance, and not just suddenly have them ambush you while you're in a disadvantageous situation.
It's a bit more troublesome to keep mobs away from you in the nether in general, if I remember correctly.
Despite the whole zone appearing rather bright, mobs can spawn anywhere and everywhere (that isn't too close to the player unless it's behind a corner, wall, pillar etc.) which, combined with the GoG mob's long lines of sight, leads to foes attacking out of the blue (or in this case, out of the red) rather often.
My suggestion? Paranoia. No, seriously. If you're anywhere that mobs can be, keep your ears tuned and don't look one single direction for more than three to five seconds without stopping and looking around and you're much less likely to get ambushed, at the cost of slightly reduced work efficiency and slightly increased pulse.
And if you're going to build a bridge, it's probably for the best if you do it properly. I'm assuming it was just a one block wide bridge, because that's the fastest and most material efficient build (although that's somewhat dangerous and not really recommendable even in vanilla). I recommend at least two blocks wide plus walls at least two blocks high on either side. If it's going to see regular use, anyway. You can cut out two whole lines of material by having the walls floating diagonally adjacent to the bridge floor, rather than actually being directly attached to the bridge floor.
The pattern, seen from the front/back, would look something like this:
B = material block
A = air/blank space
That will make it wide enough to comfortably fight on, if needed, and wide enough for mounts to fit across as well. The walls will provide (relatively, if they are, indeed, only two blocks tall) sufficient protection against both projectiles and lines of sight. Such a bridge could also be upgraded in a couple different ways afterwards as well.
It could be upgraded with torches, which will still keep mobs from spawning in the nether as usual if I remember correctly; I would place them along the top (not the side, or they could be broken accidentally if a fight occurs) of one of the walls (unless the walls are more than two blocks tall, then you would want to place them along the side of one of the walls, three blocks above the bridge floor), spaced eight blocks apart (ten if you want to be stingy, but that may let the light level get low enough for some of the bridge's blocks to have a very low but still possible spawn chance).
And it can also be upgraded with a rail line, if you're so inclined, for very fast, food-efficient travel from one end to the other. I would, however, not recommend placing a rail line without also upgrading the bridge with lighting as that sounds like a great way to suffer reverse drive-bys.