Still a little groggy today? It's only natural; you lost a full hour of sleep yesterday. Put another way, you lost slightly more than 4% of your day on Sunday. As I can personally attest, such losses are never fun. I lost about 4% of the value of my portfolio the other week during the "Shanghai Surprise," which whacked the U.S. market as well.

The combination of these two 4% losses got me thinking that Daylight Savings Time is a good time to review your portfolio holdings. Think of it as a regular necessity -- just like you're supposed to check the batteries in all of your smoke detectors every time the clock springs ahead or falls back an hour.

In my case, I used the opportunity to review why I'm invested in some of my core holdings, which include IBM (NYSE:IBM), Intel (NASDAQ:INTC), Headwaters (NYSE:HW), and Suntech Power (NYSE:STP). In each case, I remain satisfied with my positions, although I've noticed that as result of Suntech's recent run-up, I'm now more invested in energy-related stocks than I should be. I intend to sell off some of the stock (although not until after the 10-day waiting period that all Fool writers are required to abide by when writing about stocks. See disclosure policy).

My review has also caused me to reevaluate my investments in St. Jude Medical (NYSE:STJ) and Boston Scientific (NYSE:BSX). Over the past two years, St. Jude company has been essentially flat, but I remain satisfied that it's still a solid investment. Boston Scientific, on the other hand, has dropped 30%+ since March of 2005, and I'm not encouraged by its future prospects.

I can handle 4% drops. Thirty-percent plunges, however, leave me feeling more than groggy. In fact, they leave me feeling angry at myself for not reviewing my rationale for owning the stock a year ago.

Intel is an Inside Value pick, while Suntech Power and Headwaters are Rule Breakers selections.

Fool contributor Jack Uldrich owns stock in all of the companies mentioned in this article. The Fool has a strict disclosure policy.