The most senior Catholic leader in England and Wales was forced to leave a ceremony at Westminster Cathedral early.
A statement released by the Catholic Church said the 73-year-old had since been seen by a doctor. It did not disclose the nature of his illness.
Cardinal Nichols has been deemed unfit to give evidence to the Independent Inquiry into Child Sexual Abuse as planned this week.
The statement said he was "keen" to make representations concerning his time as Archbishop of Birmingham.
His appearance he been rescheduled for 13th December.
<blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">Honoured to receive this medal from <a href="https://twitter.com/PolskiSenat?ref_src=twsrc%5Etfw">@PolskiSenat</a> presented by <a href="https://twitter.com/Anna_M_Anders?ref_src=twsrc%5Etfw">@Anna_M_Anders</a> at the Mass commemorating the 100th anniversary of Polish Independence at <a href="https://twitter.com/WestminsterCath?ref_src=twsrc%5Etfw">@WestminsterCath</a> <a href="https://twitter.com/hashtag/PL100?src=hash&ref_src=twsrc%5Etfw">#PL100</a> <a href="https://t.co/2VGwbn4yrm">pic.twitter.com/2VGwbn4yrm</a></p>— Cardinal Nichols (@CardinalNichols) <a href="https://twitter.com/CardinalNichols/status/1061696016074846208?ref_src=twsrc%5Etfw">November 11, 2018</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
A week-long series of hearings are examining how church leaders, prosecutors, police and other agencies handled the abuse of youngsters by clergy between 1950 and 2000.
The statement said: "During the Remembrance service at Westminster Cathedral, Cardinal Nichols was taken unwell and had to leave the service.
"He has been seen by his doctor today who has certified him unfit to attend the hearing this week.
"Cardinal Nichols had been working hard to prepare for his evidence...He is keen to return to give his evidence once he is well again."
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