Get appropriate exercise and pay attention to your diet - this becomes more and more important as you age. Get appropriate sleep.

Do some programming on the side, just for fun if you can - you stay sharp at things due to practice, not due to innate unchangeable ability. If you're stuck for ideas, pick any online programming contest - there's a bunch that run continuously and automatically - and endless set of skill-sharpening questions to pick from and work up.

You're likely more sedentary, or not going to bed early enough to deal with when you wake up.

This is a common thing for people to start doing once they start working. Here is how you get back to sleeping normal amounts:

Stop drinking all caffeine by 17 hours before you need to awake the next day to get to work in time (so if you have to wake up at 7 to get to work, stop drinking it by 2pm; you may think it doesn't keep you up, which may be true, however it does make you sleep less deeply). Try dimming your entire house/apartment 11 hours before you need to leave for work, turning off all screens, read, listen to soft music, etc for that hour before bed. No watching TV or doing anything other than sex and sleep in bed.

Then go to bed 10 hours before you need to leave for work, have a real bedtime.

Do this for about 2 weeks, and you'll find you are so mentally alert. You'll feel like your old self in no time.

I'm curious where you got 17 hours from? I've been cutting caffeine at around 5pm, but I can't help think this is later than I should.

If you're trying to make sure you're sleepy enough to fall asleep 9 hours before you have to go to work, and you look at the half-life of caffeine: 4.9 hours on average (with a huge personal variance).

If you want to be "uncaffinated" when you fall asleep (which is hopefully <=8 hours before you get up, and a good 10 hours before you leave for work), you get less than 2 half-lifes, aka you get to drop your blood caffeine level to only 25% of what you had when you stop drinking it. Remember, caffeine not only causes you to stay awake, it causes your sleep to be less deep than it otherwise would.

Additionally: Effective use of caffeine means never drinking it in the morning (the only thing caffeine helps with in the morning is treating caffeine addiction. It's an antagonist of adenosine receptors, meaning it makes it so this chemical, which doesn't show up in your brain till late in the day, can't make you sleepy).

If you find caffeine helping you at all in the morning, you need to dial back your caffeine usage. It only starts becoming effective near 5-6 hours after waking up, and it's effectiveness skyrockets as the day goes on. So basically it takes less and less to keep you up the longer you stay awake (and has almost no effect to keep you up before a few hours awake, so morning coffee is somewhat silly).

If you are trying to get the adrenaline surge you can get when: 1. Not a caffiene addict, and 2. an occasionaly drinker of strong coffee, just do a few jumping jacks (like 4-9). It will do the same thing to your heart and you'll have caffeine as an effective tool around noontime which can be used to keep you awake the rest of the day at work, yet not interfere with your sleep.

For more information there are plenty of books on amazon.com on these topics.

I would also try meditation, there was several recent articles about how quickly (like 4 days) ones mind becomes 'sharper' from just a little bit of daily practice.

Make sure you are doing something productive with your time. If you want to get it sorted out before getting a job, try freelancing, consulting, tutoring or volunteering. Be around other people and feed off their energy. Doing nothing productive with your time will make you depressed and could definitely be the cause of a cloudy mind.

1) Program again, as much as possible. Like any other skill, you forget details of things as you spend time away from programming. Sharpen up again by programming some more.

2) Vitamin D is key in being able to focus, make sure you are getting enough vitamin D... this is true for eating well and getting plenty of sleep in general :) And lay off the pot ;P

So, everyone seems to be acknowledging the fact that your mind isn't as sharp as it was (maybe I missed a comment).

Thing is, it's simple. No, don't acknowledge it. Sure, there are hardened synapses, but to a large extent that's just an excuse for people to feel sorry for themselves. O_O

So basically, just get over the fact that you think your brain's not an sharp as it was. It's a load of crap. It's still all there, and you need to just overcome to emotional inhibitions that are getting in the way of you using it.

University is a pretty safe environment for exploring --as it should be; that's its purpose if nothing else. As a result, you're pretty well emotionally oblivious to the "what-if fears" of putting everything --all your mind and all your passion- into what you do. Perfect.

When you depart, a profoundly unseen transition takes place; you don't have that environment anymore. So you continue with the momentum you had for a while --couple months, 10 years- and then it's gone. You're learned a new environment that pulls into your mind before everything else a whole mess of things; the clichés of "only what's good enough" and "dreams are just dreams."

And then there's the "age 27 factor" as I've coined from the film Proof. (actually, go it is. It's appropriate.) :) Look back over old work and you think you realize that you'll never be able to do something that great again. Again, load of crap. Honestly, for myself, I'm typically looking back over old stuff and, while realizing the significant merit they held at the time and to the process of moving to where I am now, they're working in a highly limited fashion. What consistently happens is I let their singular weight become a symbol, a pristine concept for the knowledge I gained and I hold them so much more highly that what they actually are. On a personal level, that's fine. But to compare that symbol to actual work, no. Don't do it.

So here's my final thoughts on what it boils down to: Get over it. Your brain is still all there unless you've found little bits on your pillow. It's only a simple emotional inhibition that's preventing you from actually using your brain. Don't blame it on anything else. And finally, your old work wasn't that great. (ok, so maybe it was, but it's not nearly as great as you're holding it.)

That's it. :)

I recommend learning a language or 5. Ocaml, Erlang, Lojban, Japanese, Quenya, etc. Use Mnemosyne and Smart.fm for quick, cumulative study sessions, translate webcomics and such, play golf with old programs in new and differently powerful languages.

Also, read more. You'd be amazed at how many great SF novels you can read in a year, or how quickly you can devour Misner's Gravitation at a few pages a day.

I think the overwhelming point of all this advice is to have fun. Do things that induce flow.

Often I find that when I'm not into what I'm doing in my life at that time, I begin to lose the mental energy to form brilliant, creative, highly structured thoughts. Once I get "the rush" again, I can barely turn off the spigot of my thoughts.

Perhaps take a week in a very different setting and reconsider what you're focusing your attentions on.