Just when it looked like the banking sector was leveling off from the power dive it went into last Wednesday, down it goes again, taking Citigroup (NYSE:C) along with it. The superbank is already down 0.50% on the day. This is a hangover from last week, and it's lasting longer than we'd like.

Market roundup
First, here's where Citi's peers and the rest of the market stand on this first day of the trading week:

  • Bank of America (NYSE:BAC) is down 0.17%.
  • JPMorgan Chase is down 0.40%.
  • Wells Fargo is down 0.44%

The markets are more of a mixed bag, but net out in the negative, with the Dow Jones Industrial Average down 0.46% on the day, the S&P 500 down 0.18%, and the Nasdaq Composite up 0.13%.

Foolish bottom line
Last week, things were going along swimmingly until Wednesday morning, when B of A reported earnings. Based on how the market reacted, you'd have thought it was the worst quarter ever, but that was far from the case: Results were solid, if not stellar, and far better that B of A investors probably had the right to expect.

But it tipped the banking sector -- along with the markets -- into a dive. The S&P 500 lost 2.1% for the week. Goldman Sachs (NYSE:GS) alone lost 7% off its share price and had reported strong first-quarter earnings just days earlier. Citi investors had also gotten a glowing first-quarter report on Monday, but once the B of A effect took hold, that was that.

On Friday, it did briefly seem like investor optimism was about to take hold again, with many stocks getting back a little of what they'd lost in the previous two days, but investors seem to be in a pessimistic mood again today. All told, in the last five days, Citi investors have lost 2.48% of their related wealth.

This is one of those many times when the market is behaving irrationally. Citi had a good first quarter, and the superbank's investors need to stay calm and carry on. The market will have its ups and down, but so long as you have faith in the fundamentals of the companies you're invested in, your money is in the right place. That's what Foolish investing is all about.

Fool contributor John Grgurich owns shares of Goldman Sachs, Citigroup and JPMorgan Chase. Follow John's dispatches from the bleeding heart of capitalism on Twitter @TMFGrgurich.

The Motley Fool recommends Goldman Sachs and Wells Fargo. The Motley Fool owns shares of Bank of America, Citigroup, JPMorgan Chase, and Wells Fargo. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a lovely disclosure policy.