"Where are the sellers?" Cramer asked. "It's almost as if people decided Covid is over. It's a 'V-shaped' rally, and you better get on board."
The Dow Jones Industrial Average was up another 200 points early Monday after surging 829 points, or nearly 3.2%, on Friday.
"The Friday rally, as sweet as it was off the employment number, has not brought out any sellers. I often think that there has to be sellers at a certain level," he said.
Cramer acknowledged that states reopening their economies is bullish for the stock market. He speculated on whether people are feeling "safe to buy stocks" because they are feeling safer from the coronavirus. However, he warned, "It's as if whatever happened has vanished. Kind of like we set the world back to February."
The tech-heavy Nasdaq on Friday topped its February intraday all-time high, and closed just shy of a record.
From their March 23 lows, the Nasdaq and the Dow were each up more than 48%, as of Friday's close. However, the Dow was still more than 8% away from its record.
Cramer said, "The rallies are crazy" in beaten-down banks and airlines.
"Those runs are absurd," he said, pointing out that not too long ago buyers of banks, airlines and other economically sensitive stocks were nowhere to be found.
In addition to Wall Street betting on the reopening trade, money also keeps pouring into stocks on the back of the Federal Reserve's massive monetary stimulus, including open-ended asset buying and near-zero interest rates. The Fed begins its two-day June meeting on Tuesday.
"Either people were really wrong selling, including Warren Buffett with the airlines, or it's fanciful," Cramer said, referring to Buffett's Berkshire Hathaway revealing last month that it sold in December its $4 billion stake in airline stocks, which had included positions in United, American, Southwest and Delta.
Cramer questioned whether investors are jumping into a market "being pumped up" by the Fed, feeling they have no choice because they missed the early part of the rally.
The "Mad Money" host talked about how tough it's been to call this market, pointing to what longtime hedge fund manager Stanley Druckenmiller said Monday morning on CNBC. Druckenmiller told "Squawk Box" that he's been "humbled" by the market's rally and that he underestimated the power of the Fed.
Druckenmiller, founder of the now-closed Duquesne Capital hedge fund, said he only enjoyed 3% of the market's more than 40% advance from its March lows because he was "far too cautious" as states were starting to lift their coronavirus restrictions. He said he "missed a great opportunity here."