What should a patient suffering from severe asthma, a severe cold, and a high fever do if he performed tayammum for Fajr prayer while in a state of major ritual impurity (janabah), then went to his work where there is no bathroom for bathing, but there is water for ablution? Should he perform tayammum again, or perform ablution, knowing that he is still in a state of janabah?

If you are in a state of major ritual impurity (janabah (definition)), it is obligatory for you to perform ghusl (definition) (full ritual bath), even if it requires heating the water. If you are unable to do so, or if water would harm you, then wash the parts of your body that will not be harmed by washing, then perform tayammum (definition) (dry ablution) for the remainder and pray. If you are able to use water later, it becomes obligatory for you to do so. If you cannot find a place to perform ghusl, then wait until you return home, and you may delay the Dhuhr prayer to combine it with Asr if you fear its time will expire. If you also fear that the time for Asr will expire before you can perform ghusl, then wash what you can of your body, perform tayammum for the rest, and pray.