In 1940, Nazi Germany, Japan, and Italy made a military alliance and signed the Tripartite Pact (also called the Berlin Pact). This act stated that if either of them were attacked by a third nation, the others were obligated to declare war on that third country in retaliation. Other allied countries signed the act shortly after, including Slovakia, Hungary, Romania, and Yugoslavia. These countries considered the United States to be the likely third country to attack, so the pact was not so subtly directed at the U.S.

German and American relations had soured considerably because of the United States alliance with Great Britain even though at that point, the United States was technically neutral. US aid to Great Britain was a particular sore spot because US defenders escorting aid to Great Britain were in an unofficial war with German U-boats and would attack them if they crossed paths (see the Greer incident). Germany was also unhappy because the UK granted military control of Iceland to the United States, the Atlantic Charter, lend-lease, and so on. In short, before Japan bombed Pearl Harbor, tensions were already running high.

Japan did not inform Germany that it would bomb Pearl Harbor beforehand. When Japan did, Hitler saw this as a great opportunity to finally declare war on the United States. Joachim von Ribbentrop, the foreign minister who signed the Tripartite Pact, said that declaring war on the United States was not needed because Japan attacked the United States, not the other way around, and it would overburden German troops. Hitler didn't think that was a problem and suspected that FDR would declare war on Germany anyway after declaring war on Japan, and wanted to beat him to the punch. On Dec 11, Hitler formally declared war on the United States.

So what occurred during those four days prior in Nazi Germany? Nothing particularly out of the ordinary, because Pearl Harbor was a surprise.

Some wonderful books go into detail on this:

Inferno: The World at War, 1939-1945 by Max Hastings

Japan: 1941 by Eri Hotta

Nazi Foreign Policy, 1933-1941 by Christian Leitz