The Subjunctive of Ignorance
In Italian, declaring what you know (sapere che) states a fact and takes the indicative mood. But declaring what you do not know (non sapere che) introduces doubt. Because of this uncertainty, negative declarations of knowledge trigger the subjunctive mood.
Waking up in a hospital with amnesia is the perfect scenario to practice expressing this lack of knowledge.
When your main verb is in the past—like non sapevo che (I didn't know that)—the dependent clause uses the imperfect subjunctive to describe a simultaneous event:
| I was groggy and didn't know that that bandage was on my head. | Ero stordito e non sapevo che quella benda fosse sulla mia testa. |
| The doctor didn't know that my bewilderment was so deep. | Il medico non sapeva che il mio smarrimento fosse così profondo. |
If the unknown event happened before your state of ignorance, use the pluperfect (trapassato) subjunctive:
| I didn't know that they had admitted me to the hospital because of the amnesia. | Non sapevo che mi avessero ricoverato in ospedale a causa dell'amnesia. |
| I was too groggy and I didn't know that the nurse had changed the bandage and the IV drip. | Ero troppo stordito e non sapevo che l'infermiere avesse cambiato la benda e la flebo. |
Present Tense
The same rule applies in the present tense. Non so che (I do not know that) triggers the present subjunctive:
| I am dazed and I do not know that this stranger is the doctor. | Sono frastornato e non so che questo sconosciuto sia il medico. |
| She is still groggy and doesn't know that her own memories are about to resurface. | È ancora stordita e non sa che i propri ricordi siano sul punto di riaffiorare. |
Remember: this rule applies specifically to negative knowledge. Once the amnesia wears off and you know what is happening (so che... / sapevo che...), certainty returns, and you switch back to the indicative mood.