Well I suck at chess, but for what it's worth I think you need to play more and more and more and more and more and etc. The more you get burned the less likely it is that you'll forget. Also, use the tactic trainers everyday. You get 3. Use them. They deal alot with those type of issues, and other good issues as well.
What to do about "tunnel vision" in chess

Beginners mostly. I think that the sheer number of possible moves at any time in a game forces our brains to shut some of them out; for beginners this is done by ignoring parts of the board and other ghastly mistakes. As patterns get ingrained into your head you start to learn intuitively which lines are useless and can be ignored without even thinking about them. Such is my hypothesis!
There's been a lot of interesting research done on the way players of different levels see the board. High-level masters see it as a single unit. Strong players see it in chunks. Weaker players see it in pieces.
Anyways, the solution to OP's problem is tactics training.

NM Heisman has some fun exercises you can try to improve your board vision.
http://home.comcast.net/~danheisman/Articles/Exercises.html

There is a concrete proposal that I didn't read on Heisman's site: Focus more on expanding the list of candidate moves. At every turn, try to come up with an alternative to the move you had planned.
He covers this in many places (Novice Nooks on Candidate moves) and much earlier in this Thinking Cap "King of the Hill" article on his website.
http://www.jeremysilman.com/chess_thinking_cap/040501_thinking_cap.html
I find that there's very little about the ills and ailments of weak-intermediate player playing that Heisman did NOT cover during his 10 years of Novice Nook articles :)
i have found that as i am learning my tunnel vision has shifted. it started as what the OP described. then, a minor offshoot perhaps, i kept droping my b and g pawns after moving my bishop that protects them early in the game. now it seems to be that i focus on my attack (especially when i am seeing a mate) and miss what is going on away from that.
The funny thing about Heisman's stuff is that I've read it all, but until I'm ready for it, it doesn't stick.
Then I'll be thinking about some mistake or missed move after a game and be thinking "Okay, here's what I could have done differently to make sure that didn't happen" and then I'll remember that I read that exact advice in Novice Nook years ago.

The funny thing about Heisman's stuff is that I've read it all, but until I'm ready for it, it doesn't stick.
Then I'll be thinking about some mistake or missed move after a game and be thinking "Okay, here's what I could have done differently to make sure that didn't happen" and then I'll remember that I read that exact advice in Novice Nook years ago.
I think we need all need to hire this guy to make sure we always do stuff :)

Tunnel vision on the board is the road to defeat in my experience. You have to "focus" on the area of the board where the fight is being waged but once you have decided on a move in that area always take a "look" around the board before you make your move . sounds simple but experienced players make those same mistakes (myself) included you just get caught up where the "action" is and you forget to take that look !
One thing that keeps happening to me over and over again is that I focus on the central area of the board and fail to observe the bishop lurking in the far corner, either lying in wait for my piece or lending support to the piece I'm capturing. I'm aware that this is a weakness I need to overcome, but I don't seem to be able to see the whole board at once. Does this happen to everyone, or just beginners, or just me?